Use the Back of Your Left Hand to Cure Slice
To fix your slice, you need to work on your grip, ball position and posture first. See How to Fix Your Slice Completely for more information.
After changing your grip and so on, we should start working on your swing positions.
Top of the Swing
The cause for a slice is the open face during the swing. At the top of your swing, if the leading edge of your club is perpendicular to the ground, your clubface is well open. You are going to have to compensate during the downswing to close the face from here.
To hit a draw or fix your slice, try the following.
At the top, try to feel like the back of your left hand is facing the sky. If you wear a watch, make sure it's facing the sky at the top.
This will make it much easier to close the face through impact for a strong draw.
You can also focus on your right hand at the top. Try to feel like the palm of your right hand is facing toward the sky at the top.