Watch the Playing In Position:Mixolydian Mode online guitar lesson by Robbie Calvo from Power Play: Dominant
Your assignment is to improvise in position over one complete sequence of the 4 Mixolydian keys. Once the full sequence is complete, shift up to the next scale pattern of the Mixolydian mode and improvise in position there for one complete sequence. Repeat this process until the track fades out. As an FYI There are 4 complete sequences. This equates to about 6 minutes of focused playing time. After completing one full track of improvising I suggest you take a break to re-focus. Here's a clue to help you with your modes, the Mixolydian sequence is A7 - C7 - D7 - E7 which means you are playing the D-F-G-A major scales over this sequence of chords. That should help a bit if you hadn't already figured it out.