Here's a tip I used to use.
Try to get 4-5 kills without dying, once you reach 5 catch your breath and go slowly getting to 10. Then on and so fourth. Tbh I sometimes will kill 4-5 guys in one spot then maneuver to the next one. Don't feel bad it took me 3 years to get my expert lol but that's cuz I was helping out folks in that time