The side mount is an intermediate position prior to taking the mount, numerous submission holds can be applied from this position.
Once in the side mount you should be able to remain on top of your opponent while they try anything and everything to escape. Resting and pushing all of your weight onto your opponent will make it difficult for them to move and even make it hard for them to breath.
If you find yourself on the bottom in this position you need to escape quickly, the next obvious position for your opponent to take is the mount which as you may know is deadly.
The simple side mount position.
In this variation your right knee should be next to or above your opponents hip. This prevents them from turning and sliding underneath you. This is a common form of the side mount so you may see it a lot in BJJ competitions.
A close-up of the knee position.
You should use your extended leg to force your chest onto your opponent, making it hard for them to move and breath.
With this variation of the side mount both knees are next to your opponent. Remember to have one knee next to or above your opponents hip.