The comparative degree (“more of something”) of monosyllabic adjectives is usually formed by adding -er at the end of the adjective, possibly with the final consonant doubled, e.g. taller or bigger, and some are irregular, such as “better” (not “gooder”). Longer adjectives are usually compared using “more” (e.g. “more expensive”, “more important”). This causes some learners to combine the two constructions and say “more better”, “more taller”, “more richer”, etc.
Such usage is wrong. When something is “better”, it is always just “better” and never “more better”:
It would make sense, syntactically, to say that if “A and B are better than C”, and “A is better than B”, then “A is more better than C than B”. Nevertheless, native speakers do not use this construction, and you should use “even better” instead:
However, this does not mean that “better” cannot follow “more” in a sentence; some English speakers and teachers mindlessly mark “more better” as a mistake without thinking about the actual meaning of the sentence. For example, it is possible to say:
No, we need more better people.
The structure of this sentence is “we need more X” where X can be anything, such as roses or better people, so the above sentence is completely grammatical; it just does not mean the same as “we need better people”.