Hey, making cool buildings is by far not so hard as it may seem. Here are several simple rules we follow, with good results.
1) Select 2-4 basic blocks to use. Derivates (stairs, slabs) are welcome if not necessary!
2) Use contrast! Dark against light (or vice versa) gives your building a nice texture, pleasing to the eye.
3) Break large flat areas (walls etc.). Make some windows, a ledge, a decorative ornament (rule #2, remember?), anything.
4) Forget 1x2 doorways and 1x1 windows. Put two doors next to each other and decorate them with pillars on the sides and a ledge above them; make the windows big.
5) Build things that stick out of the walls (balconies, ledges etc.). A flat building is something you want to avoid.
You can check out our work at our profile, we've got some nice screens there for you
