Don’t use the terminal someone made for a specific airport but not for yours. Terminals are so unique. Hence, you may reuse library hangars, unless they have a sign referring to a particular location, in that case, amending its .png is the solution. Some « librarians » like me propose « anonymous » or generic versions of towers, for instance.
Don’t use 3D grass. It’s ugly and FPS hungry. Get a nice satellite image instead.
Avoid complicated polygons with huge cracks, skid marks, and wet looks. Keep it simple.
Don’t waist you time with baked surfaces, it’s unrealistic and it will make your airport look like it was made for arcade games.
Avoid animated objects, even the well known flags, it’s FPS hungry.
Try to blend in your airport to the vicinity from orthoscenery.
Check your airports for errors, find beta testers before publishing.
The best way to start is to get a satellite image and put a 3D object on almost everything you see. The ESRI background inherent to WED is not precise enough, you don’t need ZL17 but 21.
Spend 10% of your time reading or watching tutorials.
Go on the premices everytime it’s possible and take pictures for your custom buildings.