OP, I have many, many tattoos and these are my go-to rituals (of course it depends on placement/ how long you’ll be sat for)
Dont drink caffeine immediately beforehand and definitely do not take Paracetamol/ Aspirin before (it’s thins blood and most places will make you sign a waiver saying you haven’t taken anything)
Take a sugary drink like lucozade but sip sparingly only when you need it to avoid needing the loo halfway through!
Consider what you’re going to wear, especially if it’s arms/ shoulder. When it’s cold, I have a very thin flannel shirt that I wear after a tattoo so nothing rubs and also consider what jacket/ coat you’ll be able to get on with restricted movement. Wear something you’re not bothered about ruining, it’s amazing where blood and ink end up, even with your clingfilm wrap!
put a towel down on the bed to sleep, if not you’ll most likely wake up with an ink imprint on your sheets no matter how well you wash the tattoo.
when you shower, only use water and no soap. Pat dry with kitchen roll, don’t use a towel and apply a thin layer of bepanthan. Only re-apply cream when the tattoo starts to feel dry, don’t oversaturate it.
most importantly, if you need a break, tell your tattooist as soon as possible. Be warned however, that it will most likely hurt more after you return from a break as it gives the area time to swell (only applicable in a long sitting)
Good luck OP!