When I would make my towns, I like to imagine being there... how would I like the village to look? If I lived in this house, where would I like my barn to be? what deco trees should I plant? an avenue always looks nice for a main road, or alternating tree species every 2nd or 3rd tree.
Leave lots of space. Add lots of clutter... crates, barrels, etc
I've always liked Paeng's idea of building a lot more market stalls and having them lay dormant - just for aesthetics... I still find I don't do this often though.
I'm one of those that Gatherer mentioned who tend to keep placing deco while the game is still playing, then realise too late that I'm about to hit a disaster...