Especially avoid anthologies (primarily poetry anthologies) that require the purchase of their book in order to be published. One reason is stated above. But the other reason is that if they require you to buy a copy, it's not because the publication is wildly successful or an elite market. Actually they do this because this is their main means of distribution and almost sole source of sales.

Avoid writing contests that charge entry or reading fees. First of all, the financial prizes are usually minimal at best. Those contest that offer "1000's of dollar in prizes," usually do so because the prizes are often distributed to several hundred individuals. And secondly the promises of prestige and recognition from winning their awards are usually greatly exaggerated. Go ahead and enter contests, but just don't waste all your hard earned money to do it.

Don't expect all editors will critique your submission (whether accepted or rejected). Most don't have the time to do so. Even those that promise to may not on occasion because of the amount of submissions. And if you are luck enough to get a critique, realize it may have been critiqued in a hastily manner. So don't take one critique as the end all statement on whether you'll ever get published.

Don't ever believe that because a submission was rejected it is totally unpublishable. They are many other reasons for a rejection letter other than "it sucked." Most publications have certain guidelines, stated or unstated, as to the exact type, content, and style of work they will accept which also affect such decisions.

Do try to find as much information on the publication you are considering submitting to. Find out exactly what they accept and what they won't. If possible read some copies of their magazine, anthology or whatever the case may be. See first hand what has made it and try to think why- is there a theme or style of writing that flows through out the publication? A certain array of topics covered frequently? Also consult books that list the markets, such the annual Writers Digest's Novel & Short Story Markets, or Poetry Markets, etc.

Go ahead and submit your poem, story or what-not to more than one publisher at time. It only increases the chance of getting accepted. And in the event a piece of work gets accepted to two or more publications, you can always select the best deal (which offers more money or which allows you to best keep copyrights) and simply decline the others. But beware some publications frown upon such practices.

Send all your submissions in proper, typed prose or poetry manuscript form with a cover or query letter. If you don't know the form or if in doubt go to the library and look it up. And find out the editor's name so you may address directly to that person and not just put "To whom it may concern" or "Dear Editor." Always a plus in an editor's book.

Make your submission look as professional and appealing as possible. Because no matter how great you write, if the submission package looks sloppy you've already got one major strike against you and may get prejudged by an editor.

Now good luck and go get published.