Not all of this will be relevant for you, but it depends upon what you're doing, the sector and particular circumstances of your employer. The stuff relating to people who aren't directly doing your old job are very relevant (I'm calling them minions because I'm taking the piss out of how I was treated as one - it's not a judgement of their job, it's a judgement upon how it feels they are regarded by Professional Staff and Management).
Notice things.
Notice who does things to help other members of staff even when it's with something that isn't directly related to their job description. Who is often seen helping Admin with large mailshots? Who is standing at the bottom of a ladder spotting the site manager and passing up screwdrivers, ceiling tiles or picks up a mop to help when there's a leak under the sink? Who has other members of staff in with them, explaining how a particular system works - not because they're the official expert, but because they're approachable to somebody who perhaps hasn't used it before and they explain it well/without making them feel small?
Notice who always seems to be sorting out the paper jams in the photocopier. And who always seems to be walking away in a hurry to use another one and leaves it for somebody else to find and deal with, rather than sorting it out. Who leaves the copier out of paper and who loads up a new ream, rather than just 20 sheets because they can't be arsed to do it properly?
Notice slight differences in tone, body language and phrasing between when somebody talks to you/other senior staff and how they speak to 'less important' members of staff. Notice if the other member of staff is being utterly polite in the face of being spoken to like they're the lowest of the low (my best not-my-manager overheard that and acted upon it) or looks tense afterwards. Ask them quietly 'Does xxx always speak to you like that? Is that how xxx speaks to you when nobody else is around?'. If you're not directly managing one or either of them, speak to their line manager - not just the one who is out of order, but also the one who is spoken to inappropriately/sharply. Don't take a 'That's just how they are, they're very dedicated' response as acceptable.
If there's somebody who [cringe, but it's important] gives the impression that they might be neurodivergent, notice whether there's somebody who they are far more comfortable around/appears to get along with. What is it about both of them that seems to be working well? Who will say 'Oh, Fred helped me with that' or 'Jen's helping Liz and Mike with the presentation because she's great at writing introductions and can make them look fantastic' and therefore is subtly telling you that a) Fred is helpful and deserves credit, b) Liz and Mike aren't solely responsible for the presentation if it goes really well, despite what they may let you think and c) Jen has skills/talents that she's not being credited for.
Be aware of who seems quite isolated, whether physically due to where they work, what they do or because every time there's an event/presentation/big occasion or celebration, they're working their backside off doing the donkey work whilst somebody paid significantly more than them smiles sweetly and says 'Oh, it's such hard work, but I love every second of it' whilst accepting the praise and gifts for 'organising' it.
Notice whether the extra fancy bits are physically done by the person claiming credit for it, or whether there's actually an exhausted minion who has been ordered to do it (on top of the rest of their workload) having to cut individual paper tablecloths for thirty tables in two contrasting company colours, put a sharp crease into every corner and finish exactly 10cm below the surface of the tables, get the second cloth perfectly centred, blow up coordinating balloons and ribbons they have to curl, apply coordinating table confetti and then not just clean it up when everybody else has gone home, but has been told they have to keep those tablecloths in pristine condition to use next time, so can't even shove them in a bin bag along with the bloody confetti that isn't already on the floor. Have an absolute ban on the use of fucking glitter curtains for events and presentations/awards - somebody has to crawl around on the floor to cut the ends of them with a pair of paper scissors to make them fit that drop. Even better, completely ban all sparkly plastic shite, balloons and stuff that is foiled. It's appalling for the planet and more hassle than it's worth for the person who actually has to make it look pretty.
Have minions' breaks (and be aware if they actually get them, as it's all too common that they're put under pressure to not take them at all 'because I never take a lunchbreak, you know) all been set at a time when there's nobody else around on break? So they're even more isolated from everybody else than if they were able to take their break when it's legally supposed to happen? Don't assume that their manager is telling the truth - check with them.
Notice the one who Everybody Loves. Does their smile actually ever extend past their cheekbones? Or does it switch off instantly when a minion crosses their path? Or do any minions discreetly change trajectory to avoid them whenever they're spotted in the distance?
Notice the positives. Who seems to be able to make something look amazing with very little backup - well presented emails, posters, even their immediate desk area? There's a possible skill there not being recognised, supported and encouraged. Whose area shows that they see the world in a slightly different way - perhaps rather than everything on email, their planning is all done on A3 with large, brightly coloured markers? Can you find out a course that might enable them to develop this skill without it having to be directly linked to their current job description? Who gives the impression of having a very technical/logical/practical approach to things or an aptitude for fixing stuff? Could they be well supported to use those skills and develop them in a slightly different trajectory to their current role? Who seems to have the ability to calm down angry clients, the IT manager, who hears a scuffle or scream and immediately gets up with a plastic cup and piece of card in their hand because they know what the There's a Spider in Here klaxon sounds like? Who automatically helps - not who charges in because they're here to the rescue and it's exciting and looks good - who automatically helps?
Be aware of the disparities in contract terms/security/pay. Great, your professional team may well have good terms, the ability to work from home or do the school run in their cars, good housing and defined progression. But what about the other staff? Is that person expected to stay for another hour after coming in early and working through lunch with no additional pay because it's what the professional staff do (and are compensated well for doing so) actually being taken the piss out of, as they're on a hugely lower wage, have no entitlement to overtime or time off in lieu in their contract and can't say no because they're actually on a fixed term and need it renewed? Are you expecting somebody who has no sense of security, low wages, no chance of progression and a very real fear of not making the rent at the end of the month to agree to a two hour wait in the rain for a bus/train/bus/walk, no money to get a cab and no spare cash for a snack to keep them going for another four hours to work for free because 'well, we have to do it unpaid too, it's the needs of the business'?
Notice if somebody looks tired, a little drawn, has lost weight (don't necessarily comment upon it directly, it might be intentional, it might not), if their clothes seem looser/worse fitting. Don't come at it from a position of 'You need to buy new clothes, it's not professional to have trousers bagging around your legs'. Don't assume that the fat person must have gone on a diet or that any weight loss won't hurt them anyhow/that the thin person looking thinner must just be naturally skinny/has to be anorexic. It's still a change, it might be something they're pleased about, related to something they've achieved outside work, they might be feeling unwell, stressed, or nothing significant - but notice it. Notice if somebody might be covering up abuse, who flinches when somebody waves their arms around a bit too much to make their point or clams up/stammers when a conversation is more confrontational/blunt. Not just women.
Notice if, for example, a male member of staff always seems to sit very close to a female one or always needs to be standing up near her/rolling his chair until they're practically touching and she can't roll hers any further away, so shifts in her seat and angles away from him. Is he encroaching upon her personal space? Is she trying to subtly put greater distance between them? Does she look a little tense whilst trying to not draw attention to it? If they share an office, does she always try to have the door open, whilst he closes it? Does she try to avoid going near the cupboard when he's around? Is her body language screaming GET AWAY FROM ME whilst she has to smile and speak to him?
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Be clear about decisions. You don't necessarily have to make all of them as long as you make it clear that the decision of the person who is does will be respected and supported. But if a decision needs to be made, make it.
Ask people 'If you were making the decision, what would you decide?' You might find that somebody in a junior/minion position has some bloody good ideas that way - and it's suggesting to them that you can see them progressing when all too frequently, the attitude is that if you aren't already a professional/manager, there's no chance you'll ever get any further so it isn't worth trying. The person who jokes 'do you know how much trouble I've gotten into in my life by thinking for myself?' is quite possibly somebody who has absolutely been pigeonholed and restricted/held back all the time. Smile back and say 'Well, here's your chance to do it without getting into trouble. What would you decide?'
I'd suggest that a Mental Health First Aid course is a good idea. Not just for you. Who is the First Aider? Do they actually want to be or is nobody else willing to do it? Does it restrict them from doing something else like leaving their desk?
Ugh. That turned into more of a brain dump than anything else.
Tl;dr: Notice what is going on around you, behind your back and isn't thought of as important. Make decisions but encourage confidence and suggestions from everybody, not just the 'important' people. Encourage development in all, not just the 'important' people. Don't hide away in your office and only speak to somebody when you want to bollock them for something. Speak to other managers for the benefit of their team members as well as your own.