Unless you plan on experimenting with cash crops using aquaponics in your basement, you are going to need to start paying attention to dirt. We are dependent upon soil every time we put a fork to our mouth. Get the soil right in your garden and the rest — while not exactly easy — will go far more smoothly.
Like carbs, proteins and fats for people, plants have three chemical macronutrients: Nitrogen, Phosphorous, and Potassium. With the right amount your garden will grow like the Amazon; in the wrong amount you'll more likely have the Sahara. Most fertilizers come in a ratio of around 5-6-5, meaning 5 parts Nitrogen, 6 parts Phosphorous, and 5 parts Potassium. In addition, garden plants prefer a particular pH level, typically around 6.5-6.8. Your local cooperative extension agency can help you test for pH and offer a recommendation on the amount of fertilizer you may need.
You can also test soil for pH and NPK levels with a home testing kit (available at most garden stores). While it is nice to let the professionals do it, home testing can usher you back to the joy of a childhood chemistry set.
As gardeners learn more about the importance of soil microbes some are also turning to soil microbe tests. Still in their early stages, these tests identify the various bacteria, protozoa and nematodes living in your soil. Most testing facilities will provide information on how you can improve your soil ecology so that the plant feeding microbes will flourish.
Once you've had your soil tested you should have a good idea what you need to add. There are a wide variety of fertilizer options, but the best way to supplement the soil is with old fashioned products like manure (N), fish bone meal (P), and potash (K). You can also buy rock phosphate, but the mining of it is destructive and you can supplement nearly as well with fish bone meal or high P bat guano.
Adjust the Soil — With Compost
Many gardeners are turning away from a straight chemical approach and are focused on giving life to their soil. The thought is that if you develop a rich soil ecosystem the chemical balance will take care of its self. Teaming with Microbes: The Organic Gardeners Guide to the Soil Food Web by Jeff Lowenfels is an excellent in-depth guide to this approach. For the basics, just think compost, lots of compost. Each handful of compost contains billions of microbes which will go to work in the soil to create a place vegetables will love to grow.