Round turn and 2 half hitches does the job most of the time. Otherwise as said above a Bowline is good if you don't want it to slip or get tight.
Largest problem I have observed in tying down aircraft is that they leave the rope slack - very slack. May as well not tie it down!
The secret is to how little slack. Tight is often better.
Army procedure used to be pull it tight with one foot on the rope at the ground end - width of boot was the slack - would be less for a low wing.