Okay.. well I could sit here and write about 20 paragraphs about this, I will try to sum it up..
Make unique houses, but not so unique that they don't even look like houses, or that they look ugly. Don't use the same look for every house in your town.. especially don't just copy the house, paste it somewhere else on the level, and change a few tiles.
Make a nice path.. not brightly colored, not a vibrant confusing pattern.. even dirt paths work fine.. don't make straight lines for paths, but don't make them so jaggy they don't even look manmade. (just a little uneven)
Use things for decoration, but never make the decoration so overwhelming that it blocks important pathways or makes it hard to get around.
The most important thing.. take time, add details, make adjustments.. Add things like smoke from the chimneys, npc doors, rooftop patios, underpasses, etc.
