I made a LOT of mistakes on my very first custom. Actually I made so many I had to start over and found even more mistakes later! Best advice I can offer is PLAN your design. Have at the very least a basic idea of what your going for, otherwise it will run away from you and it will be a mess. Also if you don't know what materials to use, look it up. Some things such as spray sealers/paints will stay sticky for life! Don't be afraid to spend a little money on paint. Applebarrel may be cheap, but you get what you pay for. Overall, read the tutorials, relax and have fun