Gripping the bow is one of many aspects of bow shooting that need be performed exactly in order for the shooter to achieve maximum results. Before the grip can be attempted, however, there must be some understanding of how the bow works.
Basically a bow really amounts to no more than a teeter-totter balancing around the center point of the handle. The important point for properly gripping the bow is finding the correct center point. The goal is to get the limbs to bend backwards evenly throughout the draw, such that when the arrow is released the limb tips slam home at the same time.
The simplest way to determine correct placement on the bow handle is to stand in front of a mirror while drawing. Careful not to use an arrow while do this exercise. Also do not cant the bow while performing this step, instead hold the bow perpendicular to the floor. Experiment with different hand positions until you find a position that allows you to draw the bow to the description outlined above.
There are a few differences to be noted between the recurve handle and the longbow handle. It's important to keep those differences in mind while performing this exercise.
With the recurve handle you generally have more of a pistol grip. A well made bow will be designed to guide the hand directly onto the bow's center. Generally this requires a slightly higher wrist that facilitates a more "pointing the index finger" style position. This works well when shooting the bare bow as you simply need point to what you want to hit.
The longbow is slightly different and generally requires a lower wrist grip necessitating more heal pressure in the grip. This also moves the pivot point further away from the arrow rest meaning that canting the bow causes greater movement in point of impact than what happens with a recurve bow.
Take your time with this experiment and make sure you have the exact center of the bow before getting comfortable with the grip. Once you get the grip figured out, you may want to make a mark on the handle somewhere to facilitate repeatedly positioning the hand in the same place. Tennis racket grip works wonderfully for this.
Don't get to concerned about regularly shooting and good accuracy until you get a consistent grip on the bow. Once you have that consistent grip you will enjoy improved shooting accuracy.