Is there a calendar of maintenance tasks that need to be performed on fruit trees? For example, when do I prune them, when do I fertilize them, etc. If it helps, I live in the San Francisco Bay Area and am growing apples, pears, oranges, grapes, pomegranates.
Pruning typically should be done when the tree is dormant (fall/winter/spring). I think most prefer the spring, but winter might have advantages. It's not uncommon to prune trees soon after they break dormancy. Anyway, one reason for pruning while the tree is dormant is so you can see what you're doing without leaves everywhere.
I've heard a rumor that trees store their strength in the roots while dormant (so, pruning won't remove this beneficial strength from the tree then), but I don't know if this is true. This link provides advantages to pruning while dormant (I'm to tired to list them now: someone else feel free to).
Many believe fruit needs to be thinned if there's a lot of it growing on the tree. Organizations with orchards seem to have a regular schedule of when to do what (but it may rely more on how far along the fruit is than the time of year for such as thinning). You could always visit such a place, and take a tour, or volunteer, asking questions while you do so.
Fruit trees generally can be fertilized between early spring (after the buds come forth) and early midseason. Do not fertilize when the trees are starting to go dormant. I wouldn't do it within a month or two of harvest, either. (It's my belief that nitrogen has a negative impact on taste if applied near harvest time, although some may disagree that there's sufficient evidence for this.)