Angle isolation is all about not getting shot in the back. It sounds easy in theory, but in intense situations it can get quite tricky.

Novice

First thing to get started improving your angle isolation is to use cover for your back. If enemies can come from two different spots, you play close to cover, look one direction while your back is covered from the other.

 

Holding an angle

By using the boxes as cover, we cannot be spotted from winow or tunnels. In this spot we fight anyone coming out door.

Peeking

When pushing, peeking into or holding an angle, we want to be covered for enemy peeks from as many positions as possible. The pictures below show two different ways of peeking sandbags.

The angle at sandbags is not isolated, as someone can peek us from tunnels.
By taking one step back before peeking sandbags, we have isolated the angle. We can no longer be seen from tunnels

Intermediate

Transitioning between spots

Improving upon the novice info, we now practice switching between which of the angles we are looking and which ones we are covered from. How exactly this is done differs from spot to spot. It is a good idea to visualize (and practice in an offline server) how you want to transition between the spots for every spot that you play.

We use the box on the left to cover us from long when peeking short
If we were to simply turn and peek long, we are not isolated from short
Instead of going directly from peeking short to peeking long, we first step into this spot where we are covered from both long and short.
From the spot where we were covered from both long and short, we can now peek only long, making sure to keep the box as cover for short.