Most people, probably including you, start out bowling by using a "straight" shot. With this style of bowling, you simply point and shoot. Bowling with this style is effective, and you can in fact bowl an excellent score using it.
Even so, if you want to be more serious about bowling, or further improve your score, you'll need to learn more advanced techniques, adding more skill than luck to your game.
One of the first advanced moves most bowlers incorporate in their game is the hook ball.
By adding the hook ball to your arsenal, you gain much more control over where the ball travels, and which pins are knocked down.
The reason straight bowling can only get you so far is because you have to send the ball down the center of the lane, and hit pins straight on, while avoiding the gutters (and the dreaded gutter ball).
Few people can consistently bowl strikes with straight bowling -- often it's simple luck dictating where the ball strikes the pin, how much the ball is spinning, and how the pins fly around once hit.
More often than not, by sending the ball down the middle of the lane, you'll end up with a nasty split that is difficult to convert into a spare. Even if you do manage to nail the spare, you still won't be able to win a game against others that are able to hit strikes consistently.
That's where the hook ball comes in.
By using the hook ball, you add spin into your shot, using the spin to send the ball exactly where you want it to go.
Creating the hook is controlled by the way you release the ball.
In general, you should release the bowling ball with your thumb close to the bottom, using your fingers to give the ball some spin. With the right amount of spin, the ball should travel in a fairly straight line, until it reaches the "break point".
The break point is the spot in the lane when the ball begins to turn towards the target, leaving it's straight path. When the ball hits the break point, it should arc outwards slightly, then curve back toward the pins you were targeting.
To get the perfect hook ball, you'll need to analyze your bowling habits. You need to figure out your typical axis rotation and axis tilt -- or the amount of vertical and horizontal spin you usually put on your shots.
You can get an idea of these by the position of your hand when you release the ball -- get someone else to watch or take pictures or video of you while you throw several shots.
Once you've identified your axis rotation and tilt style, you can make appropriate corrections to your game. You can also get the best bowling ball for your style.
For a hook game, urethane balls are perfect. The texture of these bowling balls helps to add just the right amount of spin to your throw.
Once you've got the right ball, you need to practice. Learning how to hook the ball properly takes many throws, as you need to become comfortable with each aspect of the throw -- rotation, spin, location, speed.
It does take an investment of time, but once you've mastered the hook ball, you'll have a bowling technique available to you that will help you to score higher, making more strikes, and giving you a greater chance of hitting difficult spares.