Experts and BHG readers answer.
Thanks for writing. I'd start in spring like you are by using a pre-emergence herbicide such as Preen. Follow the directions on the packaging and repeat as necessary to keep weed seedlings from sprouting.
Pull perennial weeds that resprout from the roots; they won't be affected by a pre-emergence herbicide. Alternatively, you can spray them with an herbicide (either organic or synthetic).
Spreading a 2-3-inch-deep layer of mulch over the soil can help a lot, too. Any sort of mulch will do as long as it offers good coverage.
Other than that, there's nothing much you can do. Keep an eye on the areas --- walk through them every couple of weeks and pull any weed seedlings that you see. If you remove them before they flower and bear seeds, you'll have a lot fewer weeds to deal with in the future.
---Justin, Senior Garden Editor, BHG.com