I'm at the same stage as you: considering entering for the first time, having a general idea of what i want (very general...) and wanting to generate a piece of terrain I can use in games...
My approach is this:
-Start early so I have time to tweak and play around with methods and materials...
-Don't be too ambitious, I constantly have to bring my plan down to reasonable levels so the whole thing is not too daunting. I tend to procrastinate and not get started when projects are too daunting...
-Have fun! I don't care about popularity contests, but I care about making something cool that I'll enjoy playing with afterwards... Rule of cool is in full effect on this...
As far as materials go, I have a big pile of empty sprues that I intend to put to good use...
Enjoy! Good luck!