This question has mostly been answered, and is a really interesting discussion.
Don't feel bad if you never see a real break until at least the cat 3 level, that was the case for me. Around here, the cat 1 sprinters are almost always in The Break, so you have to learn how to get in and ride a break, even if you are a "sprinter."
Anyway, the only time it's ok to sit on a break is when you want to kill it. If you want it to succeed, take pulls. Length of the pulls depends on how many riders are in said break. If it's just two of you, better be longer pulls. If there's 10 of you, just pull through and pull off.
Whatever you do, don't surge when you pull through! That's super annoying, and guys at all levels do it. Just ****ing roll through at a decent speed.
One more thing: an ex-pro (domestic pro) once told me the worst thing you can do to your team is get dropped from the break, and I think it's true. Getting in the break is great, because your team doesn't need to chase. But if you get int he break, your team lets the gap open, then you get dropped, nobody is happy. If you're on the verge of getting dropped, just sit on. If guys yell at you (and they should), either say nothing, or say you won't sprint at the end - and don't. If you say you won't sprint, don't do it unless you want to be hated forever by everyone.