Answer the questions asked by the examiner. There are several good oral test prep books on the market.
Do not add more to the answer than necessary. Many examiners will give you a shovel and you dig your own hole. Best advice I know it to not pick up the shovel.
If the weight of the D.E. is known, do the weight and balance the night before.
Use current AFD and sectional chart. If you know where the D.E. wants you to fly to, do the work the night before.
Be sure you know how to use the wind side of the whiz wheel and also how to do the time-speed-distance calculations.
Know airspace and weather.
Be sure to get a good nights rest.
Study.
Have all documents and paperwork in order. Ask you instructor to double check your logbook and the FAA forms. Signatures are a MUST!
Be orgainzed. Know where to put you finger on the information he asks for quickly.
Double check the aircraft log books to make sure that the annual is up to date.
Wear nice professional looking clothing. Do not come in looking like a punk. Slacks, nice shirt, wear a belt and well polished footwear. Besure to practice good personal hygene. Do not wear aftershave, perfume or colone.
If you smoke, make sure you do not smell smokey.
It is good to wear a watch with a second hand.
Guys, do not wear any earrings or other jewerly in any peircings you may have. This is distracting.
Girls, same advise although tasteful earrings may be acceptable.
I could go on but my fingers are tired.
I have never had a student fail a checkride.
Best of luck. Relax. You will do just fine.