Have a look at this tutorial, as well as part 2 (on making a building) - it helped me a lot.
I also did many Google Image Searches for pixel buildings, houses, etc... and copied them into PDN, then zoomed in to take a look at how certain elements were constructed; this helped me with brick and grass textures. Try pasting my house picture into PDN and zoom into 800% -1200% to see the details.
Make sure to use many layers, putting each new element on a separate layer, so you can go back and correct mistakes, as well as copy/paste specific elements.
I started with simple cubes and pyramids and soon started to build up bigger pictures.
Have fun!
-CJ
Thanks for the link
Made this