Okay, random topic. I know this is completely random in a strange way, but I have some tips that have maybe been seen before that always help me in contests.
1) Be prepared for the challenge. You never know how random the main topic could be.
2) If it is a freestyle build-what-you-wanna-build contest with still a topic you MUST follow, think ahead. Think of what parts you can use or of the overall shape and looks of the creation.
3) Be fair to the other contestants. Like Flare has said, don't start ahead of time. Only use this time to prepare for the contest.
4) Use your time wisely. The contest is 30 days long and you only have to build 1 thing. Even though it may not seem like a lot to build, I'm pretty sure you'll be perfecting it for a while.
5) Think of a good time to start the build. If you want to add a lot of detail before or after you complete your creation, start early. Than as some of the days go on and you see that more detail is needed, add on. Be sure to take your pictures at the time you feel that your MOC is complete and ready.
These are some of my steps to success in contests. Permalink