Thick – It could be that the nail polish is too thick. Applying thin coats will prevent bubbles from forming. You can also try rolling the bottle between your palms as opposed to shaking it for beginning application.
Air flow – Sitting near an open window, in front of or under a fan is the surest way to bring those bubbles to the surface. So even if it’s hot and nasty, close those windows and turn off those fans.
Moisture – Always wash your hands before painting your nails but excess moisture on your nail plate means impending bubble-doom. Wait a good 5 minutes after washing and rub a piece of cotton or paper towel around the edges just to make sure.
Excess dirt/oil – A tip I picked up from a lovely MUA nail boarder is to wipe your nails with vinegar before applying base coat or polish. Unlike some nail polish removers that contain moisturizing ingredients, straight up white vinegar will clean your nail bed without leaving any residue.