This tutorial will not only explain how to make levels in MED, but also at high speed. A fairly big level at 4096x8192 can be done in about 8 hours or so with sufficient detail. The techniques described in this comprehensive tutorial are mostly devoted toward doing it at a very high speed. It has 48 screenshots to help explain the process in great detail.
"You level up the fastest and easiest if you do things at your own level and no higher or lower" - useful tip
My 2D game - release on Jun 13th; My tutorials
