A good general rule is to have the CoL (centre of lift) behind the CoM (centre of mass). If you don't, your planes will tend to flip uncontrollably. CoT (centre of thrust) is less important, that can be in front or behind the CoT or CoL. Just don't put it off to the side or it'll push your plane round in circles!

Also, welcome to the game, hope you have fun here.

There's also a good tutorial in the "ground school" (and it's even better in the beta)

Thx