Pointers:
Set your "city block" grid at an angle if you aren't playing on premolded
GW streets. Looks better.
Make different parts of the map different from each other: dedicate an area as Open Space; an area as Built Up, an area as Forest, etc.
Use logical connections between terrain features: Forests grow near rivers, or on one side of a hill. Buildings are there for a reason: road juncture, mine, agricultural operation, landing pad, etc.
Even if you don't have proper models for main features like these, use simple things as though you did: put a large walled yard behind a large building like a factory. Or, use small wall segments to make gardens next to house-sized structures.
Have a few of your difficult terrains close with the edge of the table, but otherwise leave space. Similarly, have a few pieces flush next to each other, but otherwise leave gaps large enough for tanks to move through.
Don't separate deployment zones with a very difficult obstacle (like a river). Don't separate the battlefield into halves with a river: isolate 20-30% only.
Roads might not do anything in the game, but they look great.
Set up battle damage logically: pick out a target for the strike and add craters and rubble accordingly.
Set up trenches in a logical way, to defend something (even if it is implicit, off-board). Remember that lots of trenches are for communication and moving around reinforcements, not just defending the front line. Trenches don't have to defend one player's side: they can be old or abandoned, cutting across the field at an odd angle.
Photograph your tables so you can learn from them. Also, you can do linked games on a larger "map" by shifting your old terrain to one side and arranging new terrain in the new direction.
Some of my past tables that I think worked well:
http://68.media.tumblr.com/8957776a740b83d2933d42282b7b1497/tumblr_nw3yar20vH1rpmlmyo1_1280.jpg
http://68.media.tumblr.com/b8ee7b017dff12f4077565c12fd3ce58/tumblr_o12x62ZkGj1rpmlmyo8_1280.jpg
http://68.media.tumblr.com/e5511aea51335153b6a5c09eaacd4fe4/tumblr_o75i92up0e1rpmlmyo4_1280.jpg