Progress in BF3 can be fun and easy or a problematic undertaking that during some games may make you want to just quit playing. Teamwork obviously being the key you should communicate with your squad and see if they aren't willing to shoot you over a friend request. Even if no one wants to do that try getting the squad to at least stick together and work together. Your squad mates can provide you with some good covering fire or a flanking the enemy to help advance your position. The comm rose works much better now so you should make good use of it. Thanking your squad mates can be beneficial and really can promote good moral among the squad. One really important thing should be is a mic check first off if the squad is all on friends lit together. Back when I was playing project reality mod for BF2 a mic was a required because you had to coordinate with your squad on so many tasks.
I realized from that game just how important communication is and how easy it is to have your ears blasted because no one did mic checks to correct mic position. I have had the misfortune of single handedly coming up against a organized squad and they cut me down before I knew they were there. The weapon attachments in this game allow any player to adapt to what the squad needs and any inbound threats. Of course players may switch class at any time but one should be ready to switch at the request of the squad if reason is sufficient. Hopefully by communicating with you squad's you can gain some good people to play with. While working with a squad dose not guarantee 100% success over time you should gain knowledge of what to look out for how camouflage works with the environment and overall better ways to communicate with squad mates. A major importance of having the whole squad acting together and communicating via mic is movement. If you are watching the rear of your squad position and are not paying attention to your mini map or checking back on the squad it can be easy for you to be left behind and have your movements exposed to fire without squad support.
Snipers pose some of the biggest threat on maps such as metro rush and eliminating them can be very difficult. Having never used the mortar I don't know how fare our you are going to have to expose your self to be able to put mortars on top of the snipers. I have never seen it first had but I would suspect that using a mav and spotting for mortar would be a effective way to eliminate or even suppress snipers. If this tactic would work it would give way for a squad to move up and attack from the side of the target to allow someone from the from to move in and arm the charge.