Catching waves is all about timing. If you are on a reef, it is much easier. The wave breaks in the same place and most of the time, it breaks the same way. Catching a wave on sand bar beaches can be more challenging.
The waves on a sand bar beach are part of the swell that is arriving. On anyone day, there may be three or four swells hitting the beach with perhaps one dominant swell. Each swell is traveling at different intervals which means the depth and speed vary. This will affect the waves in the swell my making them larger and faster or visa versa.
The line up on the beach usually sits where the most dominant swell and best waves are breaking. In addition to the best waves will be the occasional bigger wave that breaks further outside and the smaller swell that will break close to shore. First you have to watch the waves to see which break you want, the outside, the middle or the close to shore inside break.
If you sit in the line up, you are watching for the first ripple indicating a wave is on the way. Part of the line up is getting the right of way. One way to establish you want the wave is to start paddling toward it in a determined fashion. The surfer who establishes the most inside position (where the peak is formed) has the right of way.
The second trick is to catch the wave toward which you are paddling. There are three ways to line up on it:
First you paddle towards it and then turn parallel to it as you estimate where it will meet your board. In this process you are determining which way it will break, right or left, so that you can take that angle. Then when it is close, you angle more toward the beach and angle on the wave to pop up and ride it. You have to be watching the other surfers to see if you have the right of way or if someone is more inside than you.
The second method is to paddle to the wave and when you are close, sit up on your board and with your feet, churn your board around to get in line with the direction of the break and then lie down and paddle again.
The third method is to paddle with your tail to the wave and angle slightly so that you can observe the wave over your shoulder. You can paddle right and then left to see where the wave is and which direction it is heading and then speed up your paddling and/or kicking when it is upon you.