Accidents when changing

I've always dribbled a little bit while changing, but recently it's turned into lots of urine/even feces. My dad doesn't really know what to do to make this process any better, and I certainly have no idea while in my process of trying to learn to change myself efficiently and cleanly. Any tips for how to either stop going while changing or how to keep myself and my chasing table/floor clean when I'm changing?

Leave your used diaper inplace to cover your pants while changing or to protect the floor if you are just wearing a diaper while at home. I change on a folded up towel when I can this way if I leak juring the change the towel handles the leak and can be easily washed

I think you should use absorbent sheets or pads. Place one on the floor or your changing table and, if, possible, fold the sides so that they are higher, than the rest of the sheet.
You also shouldn't remove your dirty diaper until you prepare a fresh one and sit/lie over it. Only then untape and pull out the old diaper and tape on the new one as quickly as possible. If you're unlucky or just clumsy (as I may sometimes be), the most damage you'll do will be a wet absorbent sheet. But that's OK, right?

class case of cold air triggering pee undo diaper and leave it over after you go then change yoir diapee..... congrats on the potty un training