Soldier is a very simple class, but an effective Soldier can wreak havoc. He starts with a Rocket Launcher, a Shotgun, and a Shovel. Although you can unlock many more weapons, generally the most effective Soldiers use the RL and Shotgun. He is slow, but can deal high damage and is effective in most scenarios. Playing him will also teach you general skills for all classes, such as ammo management, leading your shots, and using your secondary correctly. Here are some general tips for playing Soldier, coming from someone who mains him:
-Aim for the feet, unless you're using the Direct Hit (which I almost never use, it's trash). The explosion will still do a ton of damage, and also bounce them into the air, allowing you to follow up with a Shotgun blast.
-To Rocket Jump, jump, fire a rocket at your feet, and press "control" at the same time you fire. With practice, you can Rocket Jump successfully. There's a map called "Jump Academy", look for it if you want to get good at Rocket Jumping.
-Always try to have a height advantage. The Soldier obliterates enemies from above.
-Pyros can blast your rockets back at you with Compression Blast, although a majority of Pyros are too dumb to use the Compression Blast. If you see a Pyro who is good at it, then use your Shotgun, as he can't reflect that. Also use your Shotgun against Scouts who are difficult to hit.
-Soldier has a small clip capacity and takes a while to reload. Don't be caught in the open without ammo. Try to keep your weapons reloaded at almost all times.
-One trick with Rocket Jumping is the "medic bomb". That's when you Rocket Jump into the air when fighting against a Medic and the person he's healing, and then bombard the medic from above. Use it, and you'll be one of the best Medic killers.
-Speaking of medics, medics are very good buddies for you. The Soldier injures himself a lot Rocket Jumping, and you are also one of the best combat classes. A good Medic can sustain you for a while. Plus, a Medic with a Kritzkreig can give you critical rockets (instakill almost anyone!).