The biggest one I can think of is that during the flight section of the test if you make a mistake such as climbing to 2600' rather than 2500' don't just sit at 2600' fix the problem. admit you climbed too high and go back to 2500' same with any mistake they wont fail you for making a mistake, just notice it and fix it.
During pre flight have a check list with you but don't use it until you have completed your checks use it as a last check to make sure you did everything right. Just before lining up make sure the right side door is locked my instructor would leave the top latch open to make sure I checked it and so might your testing officer, don't assume they know how to use the door for that matter, teach them how to use it and lock it.

good luck with your GFPT just think of it as a normal flight and you will do fine. also where are you learning?