I found this was best done using ALTs but it also worked with main leaving it in the background while working on something else. This also works to level up new characters with minimal effort to get them to 50 before starting episode play.

So you go to Defera Invasion zone and accept every mission, especially the "Assimilated Gorn" hard and Jula's "Higher ground" easy. Last I checked (and used to level up 6 characters) both those missions get completed so long as someone on the map completes it, regardless if they are on your team or not. The Assimlated Gorn is only daily but the higher ground mission can repeated almost constantly. You just have to keep you characters from AFKing and keep accepting the quest as it gets completed.

The main gain from this is XP, fleet marks and Rep points. If you have already maxed out the rep you can trade them in for Dilithum. I found this useful as I have three alt accounts (all three logged in at once on same map). That's 1500 dilithium a day for for the occasional click. Plus a reserve of fleet marks for the fleet.

Update, Just tested now and they patched the higher ground exploit. Which stinks because now it is harder to complete that mission since you don't get credit for the other deployed turrets around you or the aggroed Borg made by them. The Assimilated gorn still works, and gave a daily bonus of 55 marks. Thats 500 Dilithum remember for just standing there. If you add the ALTs to a team you can complete 4 times the missions using only one character.