There are a few ways that I've done this. It is definitely hard! My biggest problem when I first started LDing was trying to keep calm and not get overly excited and wake myself up!

Definitely, tell yourself to be calm and not get too excited. Of course, this doesn't always work. I've found that the spinning technique helps in many ways. It can change the dream, and it also kind of helps me ground myself in the dream. A problem with this though is changing the dream to the point where you forget that you're dreaming all over again!

Another thing that helps is rubbing your hands together. This can also increase the vividness of the dream and stabilize yourself.

Good luck and welcome to DV!