Don't be embarrassed. We all have them. Yet we cling to them like an old T-shirt we got back in our college years when we went away on spring break. In your heart, you know they should be thrown away. But you just can't do it.
What am I talking about? Your old manuscripts. Stories written years ago, when you were learning the craft of writing. You know the stories are good--goddamn it, of course they are, gotta just give 'em a chance!
Yes, you heard me right. You can still give 'em a chance. There's just one thing: they need to be rewritten. Big time. From scratch. Not just edited using your old words. Completely rewrite it from scratch.
These past few months, I've been digging out some manuscripts I wrote close to ten years ago. The stories themselves are good, however . . . they just need to be completely rewritten. Over the course of a month, I took one of these stories and started editing it. In the end, I only completed the first 40-50 pages before I realized I just need to completely start over if I was going to get anything else done.
Start with a blank screen or piece of paper. And write it. Just like the first time. Only this time it'll be with your current skill set, which has to be better than before.
A word of caution though: don't dwell on the past and think that you can't write any more good stories. Nonsense. You'll be amazed at what you can accomplish. If you really want to rewrite an old story, by all means do it. But don't forget to try your hand at something new too.