Rhyme
One thing people often misunderstand about rhyme is that it is easier to write good free verse than to rhyme. Unless rhyming comes really naturally to you, it is a very challenging place to start!
In order for rhyme to work, the lines must sound more or less like natural speech, and be more or less of the same length.
Rhyme either happens in a predictable pattern (like at the end of lines) or more randomly. As with grammar, all rhyme is a choice, and rhyme draws attention to itself. When you rhyme, you are saying “pay attention to this!”
“Perfect rhyme” is when a rhyme matches perfectly, like “cat” and “bat.”
“Slant rhyme” is when a rhyme doesn’t quite match, like “beneath” and “deceit.”
“End rhyme” is when the words at the end of the line rhyme.
“Internal rhyme” is when words inside the poem rhyme, but not at the end of the line.
If you use only perfect rhyme in your poem, it might sound very restricted or archaic, OR, if you are successful, it will sound playful, or emphatic, or maybe a little like a nursery rhyme.
Mixing in slant rhyme will make a rhymed poem feel more natural.
Remember, if you have to use unnatural language or structure your sentence in a bizarre way to rhyme, then you probably should not rhyme that particular poem.
Want to experiment with rhyme? Here a Wikipedia article listing a huge number of rhyme schemes.