Make sure you ask his weight so you can do the weight and balance, or figure out how much he CAN weigh and still stay in the CG limits, that'll impress him.
Some stupid things I boneheaded on mine cause I was nervous...
Remember to get the keys and clipboard from the desk...before you strap in.
Remember to remove the chalks from the front wheel...before you start the plane..or at least know the proper hand signals for chalks..as well as your FBOs freq
Biggies...
As mentioned..CLEARING TURNS...If I recall either two 90s or a 180.
If you don't understand what he is asking you to do, clarify before you do it...ie soft fields short fields...
This is no different than any other flight, and usually turns out to be the easiest, however you're so zinged up you'll sometimes forget stupid things..which can fail you..or kill you.
Such as..make sure you are cleared to land..or cleared for the option...before you get on short final...this is easy to forget in busier patterns and even calm ones...sometimes they clear you on downwind on slow days..and in slower planes by the time you make it to final..combined with the fact you've already done a ton of patterns that flight..it's easy to forget whether or not you're actually cleared, if in doubt..ask over radio.."understand cleared for the option?"
If you aren't going to make the first 1/3 of the runway..go around...no need to salvage a landing on a nice day with a perfectly running airplane.
Checklists..use them
Flight planning..you took the time to plot your tables for fuel burn and whatnot based off a certain RPM..FLY THAT RPM, otherwise you'll be "creating" wind. Forgive the pun. (creating wind means that it could be the calmest day..and you flightplanned as such yet you're still arriving late or early to checkpoints..so therefore it "must" be wind and not possibly the fact you aren't flying your planned airspeed
Don't forget your time off..otherwise you have no idea how early or late you are to your first checkpoint.
Don't BS the examiner...they'll usually let you look for something if you don't know it outright..and they will ask you stuff you DON'T know, not a big deal.
Enjoy your flight and good luck!