You have to do missions that are appropriate for your level -
Space combat - Star Wars: The Old Republic Wiki - Wiki SWTOR
I was doing Skaross at L39 (dinged a new level yesterday before I got banned for the credit dupe
) and it was giving me:
* 4400 XP
* 2200 credits
* 3 fleet commendations
...
every 5 minutes! But I can only do this for another level because at L40, this mission will start giving me only 5 XP. I have to move on to the new space missions for L40 and up (see link above). Those will start giving me more than the 4400 XP and 2200 credits that I was getting for the L34 - L40 missions.
You don't have to have the quest for it. You just keep running those same missions for your level and you get the same credits, xp, etc. everytime.