I'm horrible at it too. My main town is 3 years old this Christmas and it still looks like ****. I can't tell you the amount of times I've placed paths, PWPs and flowers only to rip everything up a few weeks later and redo it. For example, I've redone the land in front of my house with different PWPs, path layouts, flowers, trees and bushes combos, about 10 times in the past two months. (If only I paid this much attention to sorting out my real life...)
In short, it'll take a long long while before you find a style you're happy with. But here are my tips.
1. Do your research. Have a look a some pictures on google or visit other people's towns via the dream suite if you have it unlocked. Think about what you like and dislike about the towns. This will help you form an idea of what you would like to include in your town and how you'd like you're town to look.
2. Brainstorm. Have a look at all the possible PWP's that you think you'd like in your town and then have a wonder around the town and see if any places in your town stick out as a possible location for a particular PWP. For example, I always knew from the very start where I wanted the caf? and the fact that I wanted two benches in front of it. I find it easier to develop set sections of my town because then it's easier to almost just connect the dots.
3. Symmetry is life! Believe me, stuff just looks better when is mirrored. If you're going to have a street light to the right of your flower clock, be sure to stick one on the left too!
4. Patterns patterns patterns. Please don't be one of those people who chuck all types of colours and species of flowers together to created one giant field of nausea and eye pain. Plan your flowers and work to repetitive patterns. Orange Lilly, pink cosmos, orange Lilly pink cosmos, orange Lilly ....
Like is said, you'll most likely develop and redevelop areas of your town multiple times before you're even half happy with it. But keep going, you'll get there