Step 1: Weed prevention

Bare soil always invites weeds, so use ground cover plants, available for most garden situations or mulch the ground. A mulch, a few inches thick, of composted bark, cocoa shells or your own composted leaves, is one of the best methods of controlling weeds. Any weeds growing in the mulch are easily removed from the loose material. Don't use garden compost as a mulch as it may contain large numbers of seeds.
Many other materials can also be used to cover the soil surface and to prevent weed germination. Organic gardeners have been known to recommend soaked newspapers, though these look better when covered with a thin layer of soil or chippings!
You can also obtain weed-suppressing sheeting. The types that let water through are best and can be very effective if you are planting a new shrub border. These look best covered with a mulch of natural material.

Step 2: Weed removal

When weeding by hand, make sure you don't just pull the tops off the weeds - you need to remove as much root as you can, after loosening the soil with your trowel. Do this regularly and remove weed seedlings that you can easily identify, leaving others till their true nature becomes apparent. You will then build up your knowledge as well as leaving seedlings of your own plants which you can retain to increase your stock.
Using a hoe can be very effective if you are working between widely spaced plants. The correct technique is to keep the hoe blade sharp and move it parallel to and just underneath the soil surface to chop off weeds at the roots. This will only work with annual weeds; perennials still need digging out. Once you start, keep hoeing regularly to decrease the weed seed population in the soil.
Many weed killers have been used widely in the past but have eventually been withdrawn due to the damage they cause to health and the environment. The safer types are those that become inactive on contact with the soil. Contact herbicides kill only the plant material they are sprayed on - these will kill annual weeds but the roots of perennials will not be touched. Systemic herbicides spread to the whole plant if applied properly and are useful for dealing with problem perennial weeds. Take care not to get any weed killer on your prize plants or they will be killed too. Alternatively, try a touch weed killer. These are useful for weeds in lawns.
Tip: Whichever methods you use it is essential to remove weeds as soon as possible before further seed can be set.