For me it's a mix of changing mindset (i.e. it doesn't matter if I'm X or Y, I still have value) and maximising things that give me a boost even if they 'shouldn't' matter.
What I mean is - it'd be great if we were all self actualised and zen enough to agree we're brilliant enough regardless of how we look, what we do etc, but we're human and it's good to accept that sometimes we do just feel better if we feel good about e.g. how we look.
Mindset stuff
Giving myself compliments every day before bed. Forcing myself to find 3 positive things to say about myself that day. You can't say nothing (it's the rules) so on days where you've done nothing exciting, you still have to look for something and you start to notice smaller things you like about yourself. Feels stupid, gets easier
Consciously stop self deprecating. Out loud if necessary. Stop yourself - "Why are you being so rude? Would you say that to your best friend? That's not very nice!". Again, feels silly, but eventually you realise how often you can internally tell yourself something mean and often untrue. If you're really up for it, try the same but look deeper - when you said out loud to someone at work, "Oh I'm shit at presentations, haha", and you go back to your desk and say, that wasn't a nice thing to say about yourself, go a step further and ask yourself - why did you say that? Were you nervous and trying to lower expectations about a presentation you have coming up? How would a better, healthier way to say that have sounded - "I'm nervous about tomorrow's presentation, but I'm sure of the content so I'm sure any nerves won't ruin the delivery and we've all been there, haven't we?". Learn to read when negative self talk is serving a different purpose. And then start saying the alternative version instead - it's honest and nobody likes reassuring someone who's being self deprecating, it feels awkward - so it'll have the benefit of making you appear less unconfident to others
Accept praise, recognition etc. Do not deflect. Even if you don't really feel it, say thank you and smile. The urge to say "oh no no I am a terrible human with so many failings" at the slightest compliment is unhealthy and weird and yet we all do it - you don't have to be a braggart, you just have to accept credit that others think is due to you. Eventually it feels less alien, and you start to believe the good things you hear about yourself instead of only believing your own, rubbish version.
Learn healthy ways to accept failings, weaknesses, etc. Self esteem is good, but you can't always see yourself as a perfect infallible being - so learn to acknowledge missteps or weaknesses in a constructive and proportionate way. Fuck up your weekly big shop and only have pasta 6 days in a row? No, you're not a stupid idiot who can't even shop properly, you made a mistake and it's not the end of the world, download a meal planner app and it won't happen again. Screw up at work? Nope, you're not terrible at your job and deserve to be fired, you owned up to a mistake, took steps to fix it and have learned from the process.
Accept that nobody is the best at everything, or even above average. In fact statistically, half of people are below average - looks, talent, everything. Stop demanding excellence from yourself all the time and it becomes quite freeing eventually to allow yourself to just not be good at some stuff. Doesn't make you better or worse of a person - your looks or talent or whatever aren't a measure of your value. Practice saying '...so what?'. I haven't got a perfect arse...so what? I can't make an omelette to save my life...so what? I don't know what Montessori toys are...so what?
Silly stuff
Treat yourself. To whatever makes you feel good, even if it feels frivolous or silly - £££ lipstick, beautifully cut dress, fancy leather notebook which makes you feel professional at work, swanky changing bag so you feel like the Got My Shit Together mum, whatever it is. It's not frivolous to allow yourself the things that give you the tiniest spring in your step. Mine is 'having a really good pen'. It makes me feel like a person who has shit under control.
Avoid what makes you feel worse. Perfect Instagram mums make you feel like shit? Unfollow them! Hyper critical office mate always one upping your achievements? Learn to divert the conversation and refuse to play the game with them. YouTube workout video you do has a megafit size 4 instructor who makes you feel like a hideous lazybones for not being able to do 8000 mountain climbers in a row? Do a different one! It's often our instinct to assume that what we see is 'right' and measure ourselves (or find ourselves lacking) in comparison, but sometimes we're just consuming the wrong thing. It can also be helpful to wonder why we've assumed that thing is 'better' and dig into that but honestly, at first, just get rid. Why see/hear something that makes you feel shit?
Do something you're good at. Feel shit about how you look but have thighs of steel? Go and climb a mountain and revel in the glory. Hate your phone voice but craft a mean email? Complain about your shit service from the broadband company via cutting, beautifully withering email instead of stammering on the phone. Play to your strengths
The superhero pose thing from Grey's Anatomy (I'm sure Google will help if you don't know it!). Shouldn't work but somehow it does - now and then, I just do the silly little pose and for a minute, I feel a teeny tiny bit more badass.
Aaaaand lastly... be gentle with yourself! Unlearning low self esteem takes time. You're not going to get it overnight, so don't add 'being bad at self esteem' to your internal mean voice. It's a process :)