rmh

Make it lighter - always - you simply can't make it too light.
Not flimsy
lighter.
On scale types
try even harder as they are the worst types to do at a low weight
Not to confuse the issue but thicker wings don't lift better - they are more tolerant of angle of attack and can be stronger.
Flaps don't add lift (unless they increase area) they CHANGE the lift /drag relationship which reduces the need for the entire airframe to pitch up to increase lift.
absolutely flat plates can produce excellent lift -but are flimsy.
On models ,wing loading and power loading is everything - shape of the airfoil really means little except in very high speed situations.