The putting grip should be in the lifeline of the hands, not the fingers, so that you eliminate your wrists and hands from the stroke and allow your putting power to come from your shoulders
Practice swinging through to your finish position and holding for five seconds to achieve straighter and longer shots
Using a piece of string with tees attached to both ends is the best set up and alignment tool you can have, put it in the ground to represent your target line then use it to square your clubface, align your body to the target line and maintain a constant ball position