How do I get more res? If I kill a lot of enemies, if I heal/repair a lot, if I travel a lot. I seriously don't know how to be more efficient in this game and how to get resources more than my teammates.
You (and your team) gets more personal res from holding resource towers. Therefore most of what you do should revolve around capturing new extractors, defending existing ones and attacking enemy harvesters.
Killing enemies gives you points but doesn't help your team or yourself directly. For example killing off a marine near his base isn't going to do much, unless this is done towards the objective of defending a res point or preventing the enemy from getting one.
If you commander researches mines, try and buy a pack and stick them near where your resource towers are: you'll help your entire team and yourself in the long run if those mines keep an extractor active even for a few more seconds.
Try and pick up weapons dropped by your teammates as those weapons soon disappear and precious res is wasted.
You can't really get more resources than your teammates, but what you can do is help your entire team and by extension yourself. Try and go on suicide missions against enemy harvesters/extractors as denying the enemy team their res is just as important as securing it for your team.