This exercise will help you build dexterity in your fretting hand. Do each of these on every string.
1-2-3-4
1-2-4-3
1-3-2-4
1-3-4-2
1-4-2-3
1-4-3-2
2-3-4-1
2-4-3-1
2-4-1-3
2-1-3-4
2-3-1-4
2-1-4-3
3-4-1-2
3-1-2-4
3-2-4-1
3-4-2-1
3-1-4-2
3-2-1-4
4-1-2-3
4-3-1-2
4-1-3-2
4-2-1-3
4-2-3-1
4-3-2-1