When playing soldier, it is important that you are able to know where your target is going. If he heads left, you shoot in his general direction and then shoot where he is going to go. Not where he is, but where he is going. The rocket jump should give you a fairly good veiw of the battlefield, and you should be able to finish several enemies at once. It is highly recommended to use the equalizer. To be able to either run straight into the enemy or make a quick run for it is a very usefull tool.
The rocket launcher, if its the regualar or the DH,it only holds 4 rockets. This is usually enough to kill most on 2 rockets, depending on where you hit and who you hit. But as it has so few shots per mag you should not use the gunboats or the buff banner unless you have a big team around you.