Certain types of weeds can indicate problems with your soil which if corrected may eliminate or reduce those types of weeds. Visit http://oregonbd.org/Class/weeds.htm
Pre-emergent (prevents germination of seeds): corn gluten meal, sold under various brand names, has been shown to prevent seed germination as well as the chemical products sold for this purpose. Corn gluten meal should be applied in the cool of spring (when daffodils are blooming) and for even better control again in the cool of fall. It is safe and will add some nitrogen to your soil. Avoid using on newly seeded areas or just before seeding. It may be necessary to wait six weeks before planting seeds but plants can be planted at anytime.
When weeds are small scrape the soil with an action hoe, stirrup hoe, or Winged Weeder. This cuts the weeds off right at soil level either killing or weakening the weed. Many will not grow back. Unlike hoeing or tilling, this method also makes it less likely that you will be bringing buried weed seeds to the surface where they will begin to grow. For weeds that do grow back just cut them off again and again and many will die.
Organic weedkillers are available containing vinegar or soaps, and homemade weedkillers can be created by combining white vinegar with a small amount of essential oil of clove and dish soap. These weedkillers can kill plants on contact so avoid spraying desirable plants. They work best when applied on a sunny day at temperatures between 60 F and 85 F.
A newer weedkiller containing iron kills broadleaf weeds in lawns and works well on dandelions and other common non-grassy weeds. These weedkillers are rain safe in 3 hours which is another advantage over typical lawn weedkillers. Iron X from Gardens Alive! And EcoSense by Scotts are two that are available.
Do not let weeds go to seed. At the very least remove flowers or flower buds and dispose of them in the garbage.
Plant in raised beds to make weed control easier. See http://www.squarefootgardening.org
Mulch! Mulching with compost, bark, straw, or leaves adds organic matter to improve your soil and covers weeds and weed seeds which will kill some and prevent others from germinating. Compost on the lawn (just an inch) will improve soil and cover weed seeds to prevent some weed seeds from growing. Thicker layers of compost (3 – 4 inches) may kill covered weeds completely in flower and shrub beds. This works especially well when creating a new bed. For existing beds keep mulch at least 3 inches away from trunks of shrubs and trees.
Avoid leaving ground bare. Bare soil will be filled by nature if not by you. Get an area planted and/or mulched to avoid weeds from filling the spot. Groundcovers can fill areas between plants or large areas by themselves.
Plant the right plants in the right area to keep them healthier and so they can better compete with weeds. If a plant prefers sun, that is where it will do best.
Avoid or reduce tilling. Tilling can chop some weed roots into smaller pieces and spread them.
Most lawns should be mowed to 2 1/2 to 3 inches which helps the lawn compete better with weeds and will shade out weed seeds.
Weeders including the Weed Hound remove the weed along with the root and are easy to use even for older children.