Timing should be based on how much you are going to prune. If you are going to heavily prune (1/3 or 1/2), it is best to prune when the plant is dormant in winter (say, in February). Otherwise prune after blooming. The plant should recover quickly and begin vigorouos grwoth.

Future bloomage may or may not be affected by pruning. The one who makes the decision cannot speak so assume that the more you prune, the more this could reduce bloomage or stop it altogether for one growing season.

Prune limbs flush to the feeder branches without leaving lump where disease and insects can enter the plant. Use sharp clean pruners for the task.

If you want your camellia to grow larger than it currently is then just prune it back 1" inch or less. To stay a certain size, cut it back to a few inches l-e-s-s than the size you want.

To make the shrub grow fuller, pinch the ends when new growth starts leafing out.