Just a couple of thoughts from what I've seen so far...
There are good attempts but there have been a succession of common beginners mistakes...
1. Early Release: you have legs on, you're squeezing but no tap. It's common to think it won't work at all give up and try something else - don't. Reapply and re squeeze. Then keep squeezing into they give or break free of their own accord. If an opponent is on that position you have them and even if they aren't giving up they're hurting. If they want out make them work for it don't have them escape on a plate.
2. Positioning: sure the videos above are good but the key decider in any scissors is to be blunt proximity to your hips/crotch. The opponent has to be way high up between your thighs for it to work or you just won't get the right angle and leverage to apply enough pressure. If you aren't pull them in opening your legs to let them get closer then reapply the squeeze. Pressuring then with knees won't work at all.
I agree with all the points Wrstlelvr stated. As stated, don't give up on the scissor hold because the person does not give up within the first few seconds. A body scissor is a submission hold, but it is also a ware down hold as well. Whom ever is in the scissor hold has to work harder to get out than the person holding them. Also, having someone in a body scissor frees your arms whereas their arms are needed to get out of the hold. Use your arms to help get them in a position where you can get the submission.
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