-Bitmap/jpeg/other common formats
-Uses FE sprites/slight customizations
-Pre-gridded is nice, but not neccicary.
-If you want it to be used in the storyline, make a note of the area it is in
-No enemy units (easier to move them)
-No impossible traps
Here's one of mine:

Ostia-Armored Bridge
Good luck!


About that map you ordered... I was torn between a castle and woods, so I made a ruin/garden. I'll put in numbers and letters and enemy units when you OK it. The door is locked too, so you may want to see about buying a key/meeting a theif. 
