The only advice I can give is just slow down and think. When you continually rush in and get owned, its time to change it up. I prefer to play it cautious, always keeping an eye on my radar, keeping in mind where the enemy spawns trying to keep the fights on my terms, (like make them come to me where i can set. Good 'nade between their feet) and capitalizing on any opportunities I get.
For a gun, use the BR until you get a little more confident with your shots, then use the DMR, it seems to get the kills easier for me at least. Hope this helps. --- There needs to be a real life win/loss ratio for internet arguments, infact, lets make it a game. It will be called "no one cares"