Finally took the plunge.
Any advice for a rookie?
PC here.
Yep, as others have said, spot spot spot. Gives you points when the spotted object is killed/destroyed, and helps the whole team.
If you want to level up assault and support fairly quickly, you can find yourself a 24/7 Metro or Locker server. Just keep dropping health/ammo boxes at the chokepoints. It may be "grindey" to do that, but you'll level up super quick.
Just got back into this last night after a long hiatus. The improvements seem to be great. Hadn't downloaded Final Stand yet, but I started it before I went to bed, and I hope to get some play time in today and Saturday. Not sure what they did, but I seem to see enemies a lot easier. Before it was "who the fuck is shooting at me?!" Now it's "oh there he is."