Some things I can recommend without getting detailed:

1) Try out a new plane when there are very few people at the flying site. There will be lower risk of injury to people or damage to property (cars) and less concern about impressing other people. You need to be able to totally concentrate on what you are doing.

2) Try to perform the first few flights in almost calm air or light wind since the object is to visually notice anything odd about the flight and ground handling behavior of the plane. Heavy wind conditions do not help flying power planes and the risk of a crash increases.

3) If you want an assistant make sure it is someone that will be helpful and not a distraction. What you don't need is someone that panics, someone that cannot follow your specific instructions or someone that keeps yelling in your ear "Roll it!". The most helpful people I have had help me remained motionless and quiet unless something odd was noticed or until I asked for an adjustment to be made to the trims controls.

4) Never believe that everything is perfect. Expect something to need adjusted.

5) When you are done with flying on the first day go over everything on the plane to make sure nothing has changed. Check all bolts for tightness, all hinges for integrity, all radio equipment for any signs of misadjustment. The vibrations in the air can not easily be reproduced in the shop so the plane has been placed in a new environment when it was flown.

I try to test fly a plane as if I were helping someone else that brought out a new plane. I try to question everything and double check everything including the deflection of the flying surfaces when compared to stick movement even though I had done so in the shop (this is my last chance to perform a check). That means I am very careful during takoff, flight, landing and try one thing at a time until I feel that the basics are being handled very well. If done right the first few flights are extremely boring and predictable because everything was set up properly in the shop.