Tip 1: Drag and drop the fps counter somewhere else. Underneath is hidden a neat little white box. Click on that to choose the (another) background color.
Tip2: You can right click on the "level bar" to disable (and re-enable) specific levels. This is great when the Roof Popping and Occlusion just won't do the job.
Tip3a: You can make tilesets which contain the same tile more then once. The only restriction (within the FO:T editor) is that you need to select an alternate tile to add it to the list. This is great to create "random" floors for desert. You choose the normal desert tiles say 80% of the time, and the "feature tiles" (with small rocks and such) fill up the rest of the tiles. This REALLY looks MUCH better then doing it manually and/or not doing it at all (the last of which can make a map really ugly).
Tip3b: Instead of making the tilesets within the editor which doesn't even save them correctly), first make a tileset with all the tiles you'll plan to use, then save it. Open it in your favorite text editor (I recommend UltraEdit) fix the quoting problem (you either need to add them or remove them I don't remember), and copy-paste the appropriate tiles the number of times you want it represented in the tileset (say you want 80% sand, have 20 tiles "with features", and 8 tiles "with normal sand", then copy paste the sand tile list 10 times to get the ratio... you get the idea, I hope :). Load the tileset, and use it.