Recently i reset from master, i'm finding it troublesome to level up above 40, if anyone could help me it would be great.
I always got a lot of XP from playing objective modes like Demolition where you can extend the time limits by blowing up the bomb sites.
Hardpoint or League Play are probably best for points. Hardpoint has the highest SPM of any game mode and League Play is 7,500xp for a loss and 10,000 for a win. Run UAV, Counter UAV and VSAT (obviously not in league, lol) and bring a couple of EMP grenades for extra points from team mates too.
Search and Destroy. The games are fast and give you 5x XP per kill. So lest say you get 5 kills in a match that is same as 25 kills in other modes. And you add to that also the other bonuses and you will level up pretty fast.