You are suppose to talk to villagers a couple of times a day, write some letters if you want to. Its a little boring but also careful with what you write because they will show other players what you told them!!
If you want them to ask for more public work projects, remove all fruit, furniture, unequipped clothing, and other tradable items and spend some time on the beach area where no one is around. Just leave it for like 5-10 minutes while in real life you can go on internet or other stuff to keep you occupied, then walk around your town village a few times and wait for one of your villagers to approach you, hopefully they will ask for a public works...
It's kinda repeatative but thats progress... steady and slow..
Also personally I don't build everything that the villagers request because some of it is fugly...
Here is a guide to what certain Villagers want depending on their behaviour personalities ie lazy, cranky, peppy etc
http://animalcrossing.wikia.com/wiki/Public_Works_Projects
