meilleur or mieux
CEFR A2 · part 2
edumaterial's parts within the level. The European framework does not subdivide them.
Futur proche or futur simpleChoosing between the two futures and forming the simple one, with its irregular stems…qui, que, où, dontChoosing the relative by its role, and using dont when the verb or noun takes de.Verbs with à, with de and with nothingKnowing which preposition each verb takes, including the ones that take none.Quantities: beaucoup de, trop de, assez dePutting bare de after any quantity, and knowing when the article does come back.Adverbs and where they goBuilding the adverb from the feminine adjective and placing it after the conjugated verb.Have just and am doingUsing venir de + infinitive for the just-past and être en train de for what is happening…The rule, in three lines
You compare with plus… que, moins… que and aussi… que. bon becomes meilleur (adjective) and bien becomes mieux (adverb).
The usual slip. Saying plus bon, because English forms «better» from «good» with no special word.
Why it catches you out. English uses «better» for both «more good» and «more well», one word for two jobs. And since English comparatives are regular apart from a handful, you produce plus bon.