From two helpful people on the Steam forum, here is a list of particle removals and optimisations.

You probably want 'Direct X 9 crit boost file by itself', unless you know you're running DirectX 8 (usually in conjunction with a config). I think that it still removes the halo effect though.

Hitting airborne targets is hard. There are three main points you need to take into consideration when shooting airborne targets.

1. The distance between you and the target.
2. The velocity and trajectory of the projectile.
3. The velocity and trajectory of the target.

Becoming an expert at those three points and doing all the calculations in your head is a difficult task for experienced players. However, most experienced players do not calculate all three of these points to make a shot - instead, they try to: minimize the impact of a variable to gain an advantage.

Distance between you and the target

Generally speaking, the closer you are to the target, the easier it is to hit them.

Knowing the distance between you and the target is important. Some distances are just too far to accurately hit an opponent in the air.

Some effective methods you can accurately estimate the distance between you and the target are: the size of the target (the smaller it is the further away it is) and landmarks/popular places (ammo/health kits spawn locations and map objectives).

Knowing the distance between yourself and the target mostly comes from experience; there is no hard or fast rule to know the precise distance between you and your target.

Velocity and Trajectory of the Projectile

In general, the faster and straighter a projectile fires, the easier it is to hit a target.

Using weapons like the Direct Hit with its whopping 80% faster than regular rockets and straight line trajectory is probably one of the easiest weapons in the game to hit people in the air with.

A good way to practice with your weapon is to find an object and guess: how long it will take for the weapon to hit the object. Try to make a mental picture of the trajectory it will take. Do this a few times each day for different areas, on different maps, for different distances until you can accurately predict what will happen.

You should get comfortable with your weapon to the point it is second nature. If you know exactly how your weapon will perform, it is one less thing you need to think about.

The velocity and trajectory of the target

The easiest time to hit a player in the air is when they stop moving vertically. Try to time your shot so it hits the player when they are at the apex of their trajectory.

If you launch a player into the air look at how much damage the player received. The amount and location of damage the player took will directly translate to their velocity and trajectory. You can easily practice this against stationary bots.