Matty,
There is no hard written rule that says a lyric must use rhymes. However, if you start to rhyme, then there are some rules to rhyming. Personally I prefer lyrics that use a rhyming scheme of some sort.
Of course the English language is rife with rhymes. We were all brought up with rhymes in some fashion. Rhymes are extremely helpful in causing a lyric to be remembered. But there are different types of rhymes as well as different placement of rhymes in a lyric.
You can use perfect rhymes : need ... weed ...beard ... weird ....
Imperfect rhymes : love .... enough .....
Asonance rhyming : (where the primary vowel sound is alike) bike ... night
Consonace rhyming : (where consonants rhyme) .... dust ...frost.....
Internal rhymes: (in a line) "Nobody seems to
care about nobody any
where"
Alliterations : (where the first consonant is in several words)
feasting on
fine
fish
Rhymes are cool and if used well can really make a lyric stand out. But you don't have to use rhymes. A lyric can be outstanding without rhymes.
There is the whole technical thing about AABB, ABAB, AABC rhyming patterns or structure. I've never been one to care about that. If I start a lyric, where ever the rhymes turn up is right where they needed to be!

Once the initial or first draft is down, then I'll go back and finesse that rhyming scheme to suit myself.
Anyway, I hope this lends a hand.
Les