Watch the Turnarounds 1 online guitar lesson by Matthieu Brandt from Jump Blues
The end of a blues progression is called a "turnaround". It signals the end of a chorus and the beginning of the next. When you solo, it helps to be clear at that point about what you're going to do; take another round or finish off.
Sometimes a player will "jazz up" a turnaround and introduce a different progression (II-V-I) or play a real weird scale on the V chord. This makes the resolution to the I chord, back at the beginning of a chorus, more distinct.
A turnaround will often also be played in a chorus that's being sung.
Be careful not to be in the way of the vocalist.