Not really specific guns and tactics to use but some useful information. Sometimes it pays to be yourself. I have learned over my years of shooting gameplay that trying to suddenly change your playstyle is most of the time one of the worst ideas you can do. More often, it pays to make small changes, over a period of time, gradually changing the way you play the game.
For example, someone who uses a super fast moving smg class, trying to all of a sudden stay back and be a sniper, looking for that one shot kill. Probably will not work out in your favor. It usually results in you being upset, bored, or just plain frustrated that your not getting all those kills anymore. I have made myself a more versatile player, using all different kinds of weapons. If your not sure what you should have set up running in league play, and get bored when no one else is around then try playing some custom games with bots, switch your classes up to something you may have never used before. And just keep changing them until you have found something you like. Once you think you may have found that perfect class take it to pub matches and try it there against live competition. As you get more and more comfortable with different weapons, perks, attachments, etc. you will learn what you enjoy most, but also (and more importantly when it comes to leagues) you will learn what is most effective for YOU as a player. Give it a shot, and let us know how it works out for you if you do take this approach!