We'll start by breaking up the Natural Minor scale into six note patterns on a single string. These are just three note groups doubled up. Each group is picked Down, Up, Down, Up, Down, Up.
|Natural Minor - (Click to Enlarge)|
Now do the same with the Harmonic Minor scale.
|Harmonic Minor - (Click to Enlarge)|
Practice playing each group in turn ascending and descending. Practice slowly with accuracy in mind above speed. Keep the motions of your picking hand and fretting hand as small as possible. As you get comfortable, gradually increase your speed.
Once you've got that down, apply the following three patterns to both scales. Once again move it up and down the scale.
|Patterns - (Click to Enlarge)|
After a while, you can start chaining the patterns together in different combinations. The next examples will help get you started. These patterns will work on any string, so feel free to move them around.
|Harmonic Minor - Example - (Click to Enlarge)|
|Natural Minor - Example - (Click to Enlarge)|