There are strict rules on the rhyme of modern poetry, which can be summarized as follows: the rhyme of a regular poem is 2468 sentences, and that of a quatrain is 24 sentences. No matter whether it is a regular poem or a quatrain, the first sentence can rhyme or not. For example:
Send it to Judge Han Zuo of Yangzhou (Du Mu)
The green hills are faintly covered with water, and the vegetation in the south of the Yangtze River is withered in autumn.
Twenty-four Bridges, on the moonlit night, where do jade people teach blowjobs?
the first 124 sentences rhyme. Another example:
the leyou tombs (Li Shangyin)
with twilight shadows in my heart, I have driven up among the Leyou Tombs.
the sunset is infinitely beautiful, buried by the coming night.
the first sentence doesn't rhyme, but two or four sentences rhyme. Generally speaking, it is common for the first sentence of a five-character poem not to rhyme, and it is common for the first sentence of a seven-character poem to rhyme. "Pingshui Rhyme" is divided into 16 rhymes, of which Pingsheng Rhyme has 3 rhymes. However, due to the change of ancient and modern tones, "Pingshui Rhyme" is no longer suitable for us to use today. What I recommend to you is New Poetry Rhyme.