Before you start anything take stock of your tools, and what you already have for garden. Then, you'll first want to clear any fallen leaves, branches, dead plants, and other compost debris from the gardens surface, then weed thoroughly. If you only have a few weeds pushing up, pull them out. If your garden has been fully invaded by weeds, break out the rototiller, or hoe, and turn the top layer soil over, and sift out the plant matter. Rotating the soil will also churn up a number of hibernating pests so you might as well get rid them now. Check any plants for slugs, snails, or aphids, treating any infestations you find. Your local gardening store will have an aisle of commercial insecticides, find what you need, but there are plenty of natural remedies like my Garlic Fire that are nearly as effective.
If last year's crop has drained your soil's nutrients, you'll need to change it before planting again. The process of changing soil includes adding materials in order to increase or modify the soil's physical characteristics. Get a soil test kit from your local center to determine the gardens pH balance. This, in addition to the type of soil you have, determines the type of changes you'll need. I bring a bag of soil with me when I go to buy the kit and save myself a return trip. Once you do have all the changes you need, it's just a matter of digging up the top 6 to 12 inches of soil, thoroughly mixing the materials in, and then raking them level. Give it a week for the pH to level out and then start planting.