Citrus doesn't need much pruning. But you should cut off dead branches. Sometimes I thin out the middle so more sunlight gets in. And mine are planted near the back steps, so I prune to keep the stairway clear. In the "Sunset Pruning Book" it says that you can prune citrus any time in frost free regions. If you have frost, then prune from spring through early autumn.

If you prune citruses, you will dramatically reduce your bloom and fruit. JCin have a good suggestion, it is better to thin them out by taking whole branches rather than cutting their tips off. Blooms are formed mostly on the season following the new growth. If you cut those off, you are throwing away the productive portions. Another way is to alternate prune some branches to keep your citrus small, and this would only reduce your fruits by 50%, but usually with bigger fruits, and still a lot better than 0% when you prune or nip off every branch.

This is a question I've also been thinking about. My Eureka lemon has its fruit growing at the ends of really long branches. The weight of the lemons pulls the branches down in these funny looking arcs. One of the branches broke in the winds we had a couple weeks ago and I'm afraid there will be more breaks on other branches. I do take out entire branches in the middle from time to time, but I've also been thinking of shortening some of the branches. My tree grows year 'round, so wouldn't it produce more fruit as the shortened branches grew again?

I live near many lemon groves,(well there used to be)the commercial growers prune them hard, they make hedges roughly 7'x 7'. I think annually. I think they grow Eureka. Lemons are differant then my oranges. Lemons fruit year round. I have seen old lemon trees cut back towards the trunk, and grow back ok. Eureka is kinda an open tree. Maybe thats why they prune commercially. Does your tree get full sun, water and fertilizer?

I have seen commercial citrus growers prune their trees using something like a giant lawn mower. This has reduced their production by 25% for the year that they pruned, but then it has other benefits to the trees. One thing that you avoid when pruning citruses is a topiary style pruning where you will nip off the ends of each citrus branch so that you can have your shape, and for those citrus cultivars where most blooms are near the tip of previous seasons growth, you are effectively throwing away productive branches. Most lemons will have blooms within the length of the branch and not only the tips, so these are less affected.

You can top cut your citrus, they will quickly recover, but this style doesn't remove the tips of each stem, so you will still have fruits. The most preferred way for me if ever I have to prune is to thin out the trees by cutting whole branches. I seldom prune my citruses, I only cut branches when they rub against the house, fence or other trees. I also prune by grafting slower growing cultivars on vigorous branches. It keeps the tree balanced, and I end up with more varieties on one tree without having to do a lot of pruning.