110-200 trees
Over 75 flowers
Not over 10 weeds
No trash
Less than ten items on the floor
No harmful pwps like the trash can, drilling rig, picnic area etc.
10 or more pwps
10 villagers, though this isn't needed
I get my perfect towns in ACNL just by planting a lot of flowers. Plant 2 or 3 flowers, walk away in any one direction til you can barely see those flowers, then plant 2 or 3 more. Keep doing that every day until you get the perfect town message.
Getting it in City Folk is a bit more difficult and usually requires you to plant trees as well as flowers. In CF I would just walk around my town and use the golden shovel to plant 100 bells (which will grow into normal trees) to "fill in" spots that had no trees. I still planted a lot more flowers than trees, tho.
Oh and also, if you shake fruit directly from the tree and leave it there it doesn't count as an item on the ground so they can be nice decoration for the ground. Just not pick them up and put them back on the ground because they then count as an item on the ground.