This video looks at the basic Omoplata. There are ton of different setups that can be used but in this video we look at using the Omoplata if your opponent is in your guard and doesn't have any posture. This can be a very frustrating situation especially late in a grappling match when your opponent is trying to stall or get a breather.
It is important to get that initial hip movement. If you reference the vide you will see that I move my hips out before I try to bring that leg in front of my opponents face. This hip movement is ultra important. You will find that it significantly decreases the amount of flexibly you need to get the foot in the correct space while also increasing the amount of leverage you have to bar the face with the outside of your shin.
I find it very helpful to initially push on my opponents face/neck when entering the position. A good opponent will not want their head to be stuffed into the pocket but honestly it's not about the head going all the way down by the hip as much as it is off centering their head (taking the head across the centerline of your chest).
Finishing the Omoplata is the most difficult part and it centers around students understanding of this as a position more than a submission. It is VERY important to move the hips away from your opponent. This will dominate the outside of your opponents shoulder and greatly increase the pressure you have.
Once you have made that adjustment with the hips it is time to rotate your knees towards the floor. The only thing that matters is keeping your opponent stationary and rotating the knees. Do not get caught up in pulling yourself up (unless it's a byproduct of rotating your knees to the floor).
Let me end in saying that I think there are better ways to finish the Omoplata (and I will be showing those too) but it is also important to look at this very basic submission also.