Trading in materials - Spinmetal, Spirit Bloom, Relic Iron - will give you 5 Marks (either Vanguard or Crucible, depending where you do it), 25 Rep, and 250 Glimmer.

The most you would want to do this is 20x a week since the max is 100 marks Vanguard or Crucible per week.

Simple math:

5 Marks x20 = 100 Marks
25 Rep x20 = 500 Rep
250 Glimmer x20 - 5000 Glimmer

To get to Rank 1 = 1500 rep
To get to Rank 2 = 2000 rep
To get to Rank 3 and above = 2500 rep