dumb and stupid have different forms for their superlatives*:

dumb
dumber
dumbest

stupid
more stupid
most stupid

Never use stupider or stupidest.

*The form of an adjective that expresses which of more than two items has the highest degree of the quality expressed by the adjective; in English, formed by appending “-est” to the end of the adjective (for some short adjectives only) or putting “most” before it. — Wiktionary

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anonymous means an author of unknown name

unanimous means complete agreement within a group

These could sound similar so be sure to choose the correct one.

Do not use and etc in a sentence.

et cetera is Latin for and so forth and is abbreviated etc.

If you use the word and before the word etc it would mean and and so forth.

It is common to use and so forth instead of etc.

Use either but or yet but not both together

Use either and or yet but not both together

For more information, click here to visit Everything Language and Grammar.

couple must be followed by of unless it refers to two people
There are a couple of bright kids in the class.

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don’t is the same as do not
doesn’t is the same as does not

I don’t like grammar mistakes in a blog.

He doesn’t like grammar mistakes in a blog.

It doesn’t look good to have grammar errors in a blog.

Grammar errors in a blog don’t look good.