Wet the soil. It's an old tip, but it's an important one, especially when your beds have been baking in the hot summer sun. For best results, water the area thoroughly and allow it to sit for at least 10 minutes.
Break out the tools. A weeding tool, which has a forked tip, is best used for tougher weeds. To use it, push it into the soil and lever the forked end against the stalk and roots. For young, shallow weeds, simply rake over the area and allow the weeds to die, then pluck them out. You can also ensure weeds stay shallow by gently stirring the soil's surface, thus uprooting newly developing weeds.
Lay black plastic or garden weed cloth. This works best in areas overrun with weeds. With time, the heat will kill the weeds, making them easier to pull and lessening their impact on the garden. Be prepared for this method to take some time (maybe up to a whole season).
Weed out seedlings. The proverbial "One year's seeding makes seven years weeding" is true. After you've cleaned up your beds, make sure to stay on top of the weed situation. Get rid of weeds when they are small and before they go to seed, and you'll avoid marathon weeding sessions in the future.
One final tip: Never lay a pulled weed on unprotected ground; the seeds could spread. Either stick the weeds directly in the garbage, or lay them on a surface covered with plastic or newspaper.