If I could give you one piece of advice that could earn you a higher rally score, it would be "know the signs!" By far, the biggest reason that points are lost is due to not knowing how to properly do the signs. It seems like such a simple task, but in reality many rally signs are very similar to others, especially as you move up through the levels. It's very easy to get them confused. If you perform a sign incorrectly, you will lose 10 points. Being distracted for a moment trying to figure out what you should do can also cause lost points.
You want to know the signs so well that you can recognize them quickly upon first glance. If you need to read the sign and study where the stop signs are or think about it much, your dog will feel that attention shift and may disconnect or falter.