The Far Side Armbar from Side Control can be a great submission when your opponent is tired, distracted or otherwise not expecting it.
The success of this move is going to depend on the fluidity of your transition as well as your proficiency at getting switching grips quickly. Some of the main things that you need to look at while doing this move.
1. Make sure you look at this move as a transition of your knee. Everything else will fall into place. This movement can be a little overwhelming, especially for new people, because there are a lot of steps.
2. Watch your base, make sure to keep your hips low and plant your butt on your opponents head when you step over.
3. Make sure to get your opponent on his/her side before you try to do this submission. In this video I show how to do it using the arm wedge. Although this is a "legit" transition for getting your opponent on his/her side it can be very difficult especially at the higher levels. When you get better at this transition I recommend doing it when your opponent is already on their side (from trying to underhook, escape Side Control or one of the many other reasons that your partner would be on their side).
4. I personally believe that you should rotate as close to parallel with your opponent as you can. This will change based on your method of finishing. There is a rather vicious version of this where you drive your knee into the rib cage and fall at 90 degrees. That is not incorrect, it is just different.
5. Make sure to get a good grip on the pants BEFORE you fall. This will stop your opponent from doing many of the common escapes from armbars.
6. Squeeze your knees together and do your best to get them pointing straight at the ceiling.
7. Try and keep that arm in the crook of your elbow. If you do this it will be very difficult for you to lose the submission while transitioning.