Common mistakes to avoid:
Make sure that you do not use hot water with yeast and sugar as hot water would kill the yeast. Use water which is hot but not burning hot.
To get good pav, kneading well is very important as kneading helps in developing of gluten in the pav and makes it stretchy and elastic. Well developed gluten is important to allow the carbon dioxide released by the yeast to be held within the dough helping it to rise.
Use a tray which has a good height. When I made pav for the first time, my cloth got stuck to the risen dough and while separating the cloth from the tray, the dough got deflated 🙁