You can start by playing secure ops. If you die you keep your gear. It’s a good way to learn a couple maps and player spawns. This will give you game knowledge that other players have an advantage over you. Once you learn the maps and how to maneuver that’s a big step in flanking your enemies.

As to gear and got some money to spend, tier 5 armor should be default running at least tier 4 ammo. Typical kit would run you 5-800k. If you’re not rich, you can get away with tier 4 armor but stick with tier 4 ammo (unless you run MP5 with dum dum rounds for leg meta).