Citrus trees typically require no regular pruning once established, save removal and correction of damage, or to control the spread into utility wires, buildings or other plants. Mature orange and grapefruit trees grown as specimens can be trimmed very lightly into more decorative or symmetrical shapes but some flowering and fruiting will be forfeited in the process. Conduct pruning on oranges and grapefruit any time of the year or immediately after fruiting if you want to preserve a harvest.
Cut away any dying, diseased or otherwise damaged branches from the trees and discard them. Make crisp cuts down to the point of healthy tissue with clean and sharp secateurs that do not harbor disease.
Shorten branches that are interfering with adjacent structures or plants just enough to create the clearance your require. Place the cuts on the bias just above a leaf node.
Cut away any vertical shoots or suckers that appear on the lower third of the trunk or within the canopy of the citrus tree. They will not bear fruit as productively as other branches, create crowding in the canopy and divert plant nutrients to unproductive growth. Make these cuts flush with the trunk or parent branch just outside of the branch collar.