Rushing is part and parcel of every combat game. The objective of Rushing is to overwhelm the enemy with a barrage of... whatever is on hand. The real-life Blitzkrieg is a good example.
For rushing to work, you need people who DARE to jump directly into enemy territory with little or no backup. You need speed. You need surprise.
Planning[edit]
Tell your team you're going to rush, and ask for support. Depending on the map, you'll need to meet a certain number of people who will help. Try to tell them at least a minute before you want to go in. This helps by letting them have time to think about what they are going to do. Brief them well. BUT DO NOT ADVERTISE YOUR PLANS ON PUBLIC CHANNEL unless you're planning a decoy.
Timing[edit]
Any time when the enemy least expects it. Rushes by defense teams usually are very unexpected. You could stay very quiet, and then suddenly dash to the enemy. Rushes at the beginning of a round are common. Remember to plan well.
Teams[edit]
An ideal rushing team should have at least have 2 groups, or 'waves'. The second wave's job is to cover the first and replace losses. The first wave should simply just run in the direction of the enemy and spam grenades and bullets. G slot, AR slot, and Fireteam leader slot should preferably be in the first wave, while Medics and snipers should be the second wave, which also should be as small as possible. Second waves should be small, but present to assist. Soldiers in first waves should be capable in CQB.
One-man wrecking crews are also possible, as one man will attract a LOT less attention then waves of troops.
Objective[edit]
If Assault can win by capturing a certain thing or reaching a certain place, you might consider sending ALL available troops to make a mad dash for it. (Stop for NOTHING) Or you might wish to get a group behind the enemy and one on the other side, and launch a Bottleneck Operation. Or simply kill everything in sight. In any case, remember you need teamwork.
Attack[edit]
Hit suddenly and fiercely and ensure only the people on your team expect it. Essentially wreak havoc. Anything not on your team should be gunned down. Run. Here, smoke grenades just draw attention. Unless your objective is parallel to that of the smoke grenade, make good use of flashbangs and frags. For the first wave, SAW guys should go first, opening up on anything they see so the ones backing him up know where to fire upon. Cut relentlessly into enemy territory and split up if needed. Second wave should cut off escape routes and stragglers. Medics should be primed to run in and provide quick medical help.
Surprise and speed are your best friends.