Play regular TDM till you're about level 35. Once you know the maps, switch to Hardcore (which compares to SWAT mode in Halo 3 . i.e. takes a lot less to kill and die). Coldblood is a must, other perks are up to you.
90% of the time I run:
Blue - Bling
Red - Coldblood
Yellow - SitRep
Best gun for regular = SCAR-H
Hardcore = ACR
These are just my opinions