Instinctively most beginners in jiu jitsu will grab a hold of the opponent's neck and squeeze it hard. Especially when the opponent tries to shoot for a double leg. There's a difference between holding and squeezing the neck and a proper guillotine however. In my most recent White belt Wednesday video I addressed two common mistakes that I see beginners make with the guillotine choke: falling back and loose grips
Of course there are other way to take the fight down when you have a guillotine locked in. My coach Thiago Abreu specializes in a third way: jumping closed guard. This secures a strong position and gives you great leverage to finish. I did not discuss this move in the WBW video because in most competitions it's illegal for white belts to jump guard. It is, however, a great weapon to have in your arsenal. Check out this video where Thiago hits the move on some high level blackbelts:
So there it is, three ways to finish standing guillotines. Even if you can't finish the submission, often you still end up in a good position, and you can even combine the choke with other submissions, like anaconda's, darce's, triangle's and even omoplata's.