Golfers who struggle with a slice shot often are playing golf with a poor golf grip. To have any chance of hitting straight you must hold the golf club in the correct way.
Check your left hand grip for right hand golfers to make sure your hold is not to weak. When in your address position look at your left hand to check you can see three knuckles. If you see less then your grip will be on the weak side. Thus encouraging a weaker shot off to the right.
Twist your left hand to a three knuckle position for straighter golf shots.