One more thing that also often trips up my students is the rhythm of the university year. There are busy and fallow times for academic and professional services staff, and if you really need a form signed or a draft read urgently, you need to plan in advance so you can work with the rhythm not against it.
In my experience - and other places/disciplines might be different - if you urgently need academics or professional services staff to do something, avoid asking during the following times:
Freshers/induction week and the first week of semester 1 (except in your first year, when you will be scheduled in).
First week of semester 2.
Christmas to New Year - this is just about the only time in the year when the entire institution will shut down.
August. This one is critical. If you need an important piece of paperwork signed, ask in July or September.
The problem with August is that this is peak season for academic and professional services staff to be away, and often completely inaccessible. Typically academic staff don't take their full holiday entitlements, but even if they are not on holiday, they are likely to be halfway up a volcano or doing fieldwork in a remote Ugandan village or in a basement archive that doesn't have wifi. And even if they are in the UK and not on holiday they will be working from home, which could easily be hours away from the department.
Also, depending on your institution, the May exam period is often crazy busy, with everyone on short, hard deadlines for marking and administering results. In my institution it's actually fine for most academic staff, but the chair of the exam board (who could be your supervisor) and the professional services team will be going nuts.
If in doubt, ask!