Know that many people say they prefer to change it standing up in front of a mirror or the sink or whatever, but I have not had luck with this. My stoma is very inverted and kind of sits below skin level, in the valley between what I would call the two layers of my muffin top. If I'm being honest, I have more of a three-tiered wedding cake top than a muffin top, but I digress. (And mentioning that makes me want cake. Darn.)
When I try to do it standing up, I cannot get the area to be flat enough or my stoma to protrude enough for me to put the seals around it correctly. Even if I'm looking in a mirror, this is difficult. For this reason, it is much easier for me to do it lying down, because gravity helps flatten things out enough for me to get the seals nice and flush around it. I have had bad skin issues since I left the hospital; right before I was discharged, even with nurse help, we had to change the whole appliance 7 times within a few hours. Thus, my skin is very damaged and sore. I have to make sure the seals and all the barrier sprays and everything are where they need to be. Because I have so many steps right now to try to heal up my skin, it's a lot easier if I'm lying down, sort of propped up, so I can see the whole thing when it's flat.
I am still on medical leave, so I don't know how this will work once I have to go back to work. I don't want to be caught lying on the floor in the bathroom stall when my boss walks in, and the seat in my Camry doesn't recline that much. But for now, that's what I'm doing. I am hoping that once I get back to work, I can work out an eating schedule and everything that will help me avoid the need to ever have to do a change at work.
P.S. At the advice of a stoma nurse I talked to, as well as many on here, I'm gently washing that injured and angry skin with Head and Shoulders in the shower, letting the skin get a little air for a few moments after that, then applying Flonase with my fingers. It's a long process at this point, but I'm sure I'll find a better routine once my skin heals up. Remember: 3 or 4 marshmallows a few minutes before your change will help put your stoma to sleep for a bit, to make your change "dryer." And I warm my wafer and barrier rings on a heating pad while I'm doing the other prep.