Don't rush. Rushing used to be a viable option in previous Call of Duties, but not this one. Use the Type 95 with 2 attachments (Red dot and rapid fire). Sleight of hand, assassin, and steady aim. I know how you feel with the transition from Black Ops to
MW3. I had a 2.9 KD in Black Ops and I used stuff like dual wield scorpions and the Olympia. In this game, however, I have a 2.4 KD and I use all the try-hard guns and perks. I only play TDM; I suggest you do the same. It's hard to do well when you're trying
to get kills, AND cap flags because Lord knows your teammates won't
camp everyone else does. I'm getting killed by snipers who just stay in a room, with one shot and by quickscopers, because assault rifles seem weaker, shotguns are weaker but sniper rifles are one hit kill, so all these idiots are running around quickscoping
no matter that everyone one in the community hate them
1. Get a gun you feel comfortable with, something which is light like the sub machine guns. Get a good attachment, red dot? Holographic, something which will give good measurement to get a good aim on.
2. Use cover. I know maps are small in the game but keep yourself hiden and have a good spot to jump out from to get a kill in Search and Destroy or domination. Anything with defence is a positive and advantage because you HAVE time.
3. Go into a private match and load up some maps, get yourself a good spot, any hiding places or places to snipe or have an overwatch of the map. Crucial to helping yourself and team mates.
4. Communication is key to winning, you need people you know on your team and that are going to help you and call out. It is going to be hard to adapt playing with 5 randomers especially with no communication what so ever.
5. Try team death match to start off with, reason for this is its easy. There is no serious or one objective to gain or go for and unlimited lives. After getting warmed up use the other game modes that are more complex like Search and Destroy. Avoid Kill
confirm and domination for now because these are extremely fast paced modes and you are likely to struggle to keep positive.
6. Perks, perks and more perks. Choosing the right class and perks is crucial to success and your own gameplay. If you hate being viewed or noticed on radar, use assassin to avoid being caught on radar. Make sure you get good weapon perks to maintain a good
kill/death ratio and comfort. And sort out your class to what you like.
Just using some of these tips will help and help you become a bit better by time and time again. Also don't mind the 1 liners saying camp, rush or whatever. It doesn't help.