I am a week in to answering questions for my new column in the San Francisco Chronicle, and notice that the largest single topic that people wonder about so far is fruit trees. Makes sense, in that they are a big investment in time and expense. They take 3 to 8 years to bear fruit, and what you do in that 3 to 8 years makes a big difference in whether you get fruit and how much. I see a lot of errors in growing fruit trees, mainly ones of omission. That is, the error of simply buying and planting a tree and then watching it grow without attention or care.
Every step in buying and caring for a fruit tree requires thought and attention if a tree is to be a good tree. Starting with choosing the tree. Some of the considerations are size (some are available as dwarfs), adaptation to your microclimate, and whether the variety needs a pollenizer (a different variety nearby to provide pollen). (I have discussed these matters in my book Golden Gate Gardening, Sasquatch Books, 1998, see sidebar of blog.)
Planting the tree requires thought, to be sure it is in a suitable place in your yard and planted in a way that allows soil to drain well if you have heavy soil.
And then ongoing care requires thought. If it is a deciduous fruit tree, most require pruning from the first winter after planting to insure that the limbs begin low enough that you can reach the fruit to harvest it and that the tree produces fruit-bearing wood. Ongoing pruning keeps the tree producing fruit by reducing unfruitful wood and keeping the branches from becoming too thick. You can learn this from illustrated books or hire someone to do it for you--worth the expense, considering the rewards.
Citrus needs little pruning, but does need careful attention to watering--deeply and not too often.
This is only a beginning, but with a little thought and care, a fruit tree will reward you for years, so its worth the trouble.
There is much information on fruit trees at http://www.davewilson.com/homegrown/homeindex.html and at the site of the California Rare Fruit Growers www.crfg.org (don't let the name put you off, they are interested in all kinds of fruit), and information on growing citrus at www.fourwindsgrowers.com.