How to master a Focus Attack in Street Fighter 4

There are three levels to the Focus Attack (Saving Attack in Japan), each with its own properties.

Level 1 FAs are performed by pressing MP + MK. After it connects, whether or not it hits or is blocked, you can immediately cancel it into a forward or backward dash. This is useful for either applying more pressure with a block string or retreating from a potentially bad situation. You can also dash cancel forward or backwards to fake out your opponent or bait them into jumping at you by holding MP + MK, performing the dash command and then releasing MP + MK after the dash animation has started.

Level 2 FAs are performed by holding MP + MK until your character flashes white. These have the same hit absorption properties as Level 1, but if your Level 2 connects, the opponent crumples and you get a free combo! You just have to dash cancel forward as soon as you see it connect. If you wait too long, they fall and if you hit them with a normal, it will pop them off the ground and reset them.

Level 3 FAs are performed by holding MP + MK until the FA is released automatically. These have the same properties as Levels 1 and 2 with one major addition: they are unblockable! It also does a pretty decent amount of damage.

Focus Attack Dash Cancels
FAs can also be used to cancel special moves into a dash. There are two ways to do this:
Do your special special and immediately hold MP + MK, then dash and release during the dash.
Do your special and immediately tap MP + MK then dash.

The engine is pretty flexible so try it both ways and see which one works for you. You can use the FADC to set up situations and combos which would otherwise not be possible.