The Mixolydian Mode

The mode is created by playing the notes of a major scale starting from the fifth note. Here's an example of the mode starting from G, based on a C major scale.

Here's the formula of the Mode:

How to use the Mixolydian mode When Improvising?

Well, the most significant characteristic of the mode is the lowered seventh. That makes this mode perfect when played over a dominant chord. If we take a II-V-I chord progression for example the mode would be played over the V degree very naturally.

An important tip: The seventh note of the mode is a lowered.
Since F is a very active note in C major scale attracting us toward E we will solve our melodic phrase from F to E as we proceed in the chord progression to the tonic. Notice that the fourth note in the mode could clash with the third note of the dominant chord when it is played over the beat. I recommend playing it only as a passing note (between the beats).

Compositions in the Mode

Old Joe Clark
Dear Prudence
She Moved Through The Fair
Let It Loose