How to effectively use the Beggar’s Bazooka

In addition to learning the maps, there are a few other things to know:

• Sentry guns beep 1-3 times each time they change directions (so about every 3 seconds). Once for mini/level 1, twice for level 2, thrice for level 3. Generally, if you can hear a sentry's beep, you'll be in its range when you round a corner.
• As a Spy, you'll get a LOT of cheap deaths. Sadly, this is because of the Spy's shortcomings in order to combat the instant-kill backstab.
  • The Spy's Dead Ringer takes some getting used to, but in certain situations, using it (preferably while disguised as a teammate so they don't know you're a Spy) can get past a defensive line. Beware that the Dead Ringer makes a louder than usual decloak sound. The Dead Ringer is a "perfect" cloak for the first 6.5 seconds, so enemies who touch you won't make you appear as a team-color outline. However, they still can't move through you.
  • The Cloak and Dagger gives you some latitude by not decloaking when you don't want to, but it also has a very short cloak time.

Having said all this, you're still going to die a lot in Team Fortress 2. It's the nature of the game! The lower-HP classes in particular are specialized in some way, but lower HP is the drawback.

While it won't provide a full and technical explanation about how to pop enemies into the air, this video shows (in a pretty accurate way) how to do so, using the rocket launcher:

The technique is basically to aim at the enemie's feet. The lighter the enemy is, the easier he'll fly away (you know who I'm talking about). And if you are lucky enough and hit the enemy while he's jumping, he will even fly higher.

Also, as for many other games, watching replays might help to catch the technique. There's a bunch of fragmovies and replays where you'll see the soldier in action, helping you to understand how to improve your soldier's air-popping skill. I'd recommand you that one and this one where this particular technique takes a good part (among others).

There are also videos about the Reserve Shooter's gameplay.