4. Salt Them
I stock up on discounted rock salt at the end of the snowy season and sprinkle it on my gravel garden paths to keep weeds from coming up in the spring (pool salt or regular table salt works as well, but it's more expensive). Salt also makes a good weed barrier along lawn edgings and other places you can't reach with a lawn mower, but apply it carefully, since it will erode concrete surfaces and can leave the ground barren for a protracted period of time.
5. Divide and Conquer Them:
Never underestimate the value of installing physical barriers like lawn edgings and retaining walls to keep unwanted weeds from invading your lawn or flower beds. Acting just like a fire-break, physical barriers are a long lasting solution for keeping weeds at bay. I make a simple and cheap lawn edging out of scraps of pressure treated decking lumbers, cutting it into 8-inch "pikes" and hammering them into the ground next to each other to form a continuous edging.
6. Out Number Them:
Gardening is all about a competition for resources, where the strongest not only survive but thrive. By choosing ground covers, flowers, and garden crops that will naturally out-compete weeds for sunlight, water, and soil nutrients, you can dramatically reduce the number of weeds you'll need to contend with. The same principle applies to controlling weeds in a lawn: by maintaining a thick, health lawn, the fewer weed-invaders you'll have.
Related: 7 Habits of Successful Gardeners