-
I would do story missions however boring they may be, but run them on the hardest difficulty you can. If you need a higher level guardian to help shoot me an invite. Doing it that way will get to almost 20 in a day.
-
I just started another titan to level up.
-
I do Earth missions first, then patrol and bounty the Earth until higher level. Once I level up until about 10, I continue to the Moon on hard and finish all missions.