Accept that rhyme purists will look down upon you. Some people have always looked down upon slant rhyme, so whenever you use it, some people will try to tell you that you are not rhyming correctly. Learn to ignore these people.
Select a word that you would like to rhyme with, such as "button" or "ninja."
Make a list of words that rhyme perfectly with your selected word. For example, "button" rhymes with "mutton," and not much else. Realize that restricting yourself to perfect rhymes will severely limit your lyrics, because if you want to talk about losing a button, you will have to try to work mutton into your rhyme.
Start looking for slant rhymes by finding words that can be made to rhyme perfectly when abbreviated or pronounced differently. For example, "button" may rhyme with "nothing" if pronounced "nuttin'."
Create slant rhymes by changing either the vowels or consonants in your target word. For example, change the vowels in "button" to get "bitten," or change the consonants in "ninja" to get "Inca." Both of these are slant rhymes.
Create additional slant rhymes by changing one of the two syllables in your target word. For example, "button" could become "butter" or "beaten."
Use extra words to create slant rhymes when no single word fits. For example, "Ninja" has a good slant rhyme with "skin ya," something that ninjas might do, or "in ya."
Combines your slant rhymes from all of these steps, as well as any perfect rhymes you may have. For example:I can't do nuttin' when I've lost a button,Ate too much mutton on which I'd bitten,Had it with butter, know it needs something,I would skin ya like a ninja but I've got to get shuteye.