When you can, "dry fit" parts together. Make sure things actually fit before you get glue involved. These days, with laser cutting and such, most parts will fit right, but you never know for sure.

Old saying: Measure once, cut twice, measure twice, cut once.

While an expereinced builder can make a kit appear amazingly quickly, don't get in a hurry, and it never hurts to double check everything you do. Sure, it will slow you down, but it could save a lot of headache.