Many of you know this already, but I'll mention it briefly for those of you who don't, because I think it's interesting, and I like poetry that rhymes.
Rhyming is much harder in English than in many other languages, because so many other languages add standard endings to words to represent gender, number, and so forth. In English you can find plenty of frequently-used words that are very hard to find a good rhyme for.
Moreover, many rhymes have been used so frequently -- first in formal poetry and later in popular song lyrics -- that by the time you reach your 30's you almost wince when you hear them trotted out yet again ("danger" and "stranger" is the classic example). The difficulty in making English rhyme often leads you to suspect that the rhymes are forcing the poet's hand, rather than the other way around.
So, the ideal of rhyming poetry is to make it seem as though the rhyme is just a happy coincidence: that you chose those rhyming words, not because they would rhyme, but because they were simply the best words for the situation. If you have to tie yourself (or your phrases) in knots to accommodate a rhyme, it's probably a rhyme you don't want in your work.