Position before submission is a common phrase in the jiu-jitsu world but what does it mean? It may not mean exactly what you think. It is a phrase that carries different meaning as you progress in your jiu-jitsu. A lot of things tend open up and carry a new meaning as we mature. That doesn't necessarily mean that what you originally thought it meant was wrong.
If I am talking about position before submission on a beginner level, I am talking about securing and maintaining your core positions like the guard, cross body, mount, back mount, exc.. and then, after wearing your opponent down, look for the submission. It is important in the beginner level that the students learn to use these positions and develop them. If you don't learn your positions, transitions and escapes, than in the long run you are going to pay. You won't be able to gain any sort of dominant position on the ones who are well versed in their positional game. You could break jiu-jitsu down into two basic categories
1. Grappling Game
2. Submission Game
The grappling game includes your take downs, positions, transitions, sweeps, passes and escapes. It has everything to do with your ability to dominate your opponent positionally and wear them down. Your submission game has to do with your ability to submit your opponents. Learning your submissions and being able to set them up and finish them. In the beginning it is important to keep these two groups separate. You need to learn your positions and then learn what submissions work in each position. In the beginning it is more important to learn to get a mount and hold a mount than it is to get a mount and try to submit your opponent. In the end, the liberty to submit your opponents relies completely on your ability to control them. The better you learn to control your opponent, the more ways you will eventually be able to submit them. One of the best things you can do as a beginner is to grapple without submissions frequently.
As an intermediate student position before submission begins to carry on a different meaning. The positions I am talking about here are the arm bar position (Spider Web), omoplata position (Rodeo Control), triangle position (Diamond Guard) ankle lock position, exc.. These positions are submission positions. In order to really develop a good arm bar it is imperative that you learn the arm bar position. In order to drill and develop your arm bar position you should start in the arm bar position...
and then tell your partner to try and escape. As your partner works to escape, your job is only to keep some variation of the arm bar position. Don't try to finish the arm bar but try to keep him from escaping. Eddie Brave calls this the spider web position and you can certainly do more than an arm bar from it. Once you get good at controlling this position you will be able to easily finish an arm bar. Most of the time at the beginner and intermediate level students don't have a very hard time getting to some sort of submission position. The problem is that they are in such a hurry to finish that they leave to much space and their partner not only escapes but usually gets to a better position. Submission position drills will take care of this issue. You should drill it frequently from core submission positions like the ones listed above.
Lastly, when I am speaking with advanced students about position before submission, I am talking about control in general. An advanced student who has perfected their core positions and their submission positions can control people in what would look like a very loose or un-secure position. Advanced students have a much better sense of feel and know how to use every part of their body to control their opponent. They begin to develop positions that a beginner could never use because they haven't developed this awareness of movement yet. If an advanced student took some one's back and sunk in the choke before the hooks it wouldn't matter because he knows how to control his opponent without the hooks. He knows how to position his body to prevent from being thrown off. He also knows how to secure a good squeeze on the choke in order to get a quick tap. It takes many hours of drilling and sparring for a student to develop this ability.
As you continue to mature in your jiu-jitsu you will begin to understand these concepts and will take them to an even deeper level than what I have explained. Turn every situation into a position and learn to master it. This is how you can learn to submit anybody!