Pro Tip: Buffer Missions for Turn-In

Technically you do not need to be in fleet with a client while doing missions for the client; you only need to be in fleet to turn the missions in. Therefore, you can effectively work for a client without being in fleet by completing several missions, but not yet turning them in, until you fleet with a client, at which point you turn them in all at once at the beginning of your grind. In effect, you are buffering missions for turn-in: you are still working for the client, but are simply turning in the missions at a time later than the work was actually finished.