If you have a skillet that always sticks, check this: Put it on a level surface and see if it sets flat, or if it tilts slightly. If it's doing the tilting, that's the cause of the problem - it's not your cooking!
Source: My own idea after having problems with an expensive skillet that wasn't made properly and which always had food sticking to it.
Also,l check to see if your stove/kitchen floor are level! The stove can be remedied by using a wrench on the riser screws on each bottom corner. The floor is another story ... maybe the stove can be leveled to the floor warp by checking if the water in a frying pan is level.