There's a school of thought that says, as soon as a story, poem or novel etc. is rejected you should send it out again. Like a boomerang, you should throw it straight back to another publisher. This is probably the best antidote to rejection, because it doesn't give you time to worry or get depressed. Your writing is your product, and as with any other business, it isn't going to enhance your reputation or improve your bank balance until you sell it.
    Those are the pros, but there are some cons to this advice too. While I wouldn't recommend allowing work to languish in a drawer indefinitely, giving yourself a chance to recover from your disappointment, so that you can consider why your work was rejected makes sense. You need time to digest any comments the reader(s) might have made, even if you disagree with them. Re-reading the work objectively might show up aspects you hadn't discovered before. If you do rewrite anything, you'll need to set the work aside so you can look at it with your editor's and proofreader's head on, and make sure there are no mistakes in the manuscript. It might be that when you re-read the work you are still happy with it, but that you can see that trying a different market might be more successful. Alternatively, you could decide to try the piece in a different format or genre.
    Sending work out as soon as it is rejected can also disrupt work in progress, and take you away from it for longer than waiting until you have a batch of pieces to send. This is particularly true if you have to research markets, even if you use a site like Ralan.com or Duotrope. Sending several pieces out at a time also prevents you worrying and waiting for a reply, as you would with an individual work.
    Try setting aside some time on a regular basis, maybe an afternoon a week, to review returned work, research markets and send work out. Always keep a record of where each piece goes and when, then forget about it until the publication's stated response time has elapsed. Publications are often optimistic about how soon they'll be able to get back to you, so give them some leeway, then by all means, query. Try not to be anxious about a delay. Hopefully, it means the publisher is giving your submission the same amount of thought that you gave to sending it.