Sit, set. Do not confuse these two words. See §57.

So. Do not use so alone as a conjunction. Say so that.

Wrong: He spoke in the open air, so more could see and hear him.
Right: He spoke in the open air, so that more could see and hear him.

Some. Do not use some as an adverb in the sense of somewhat or a little.

Wrong: He plays the violin some.
Right: He plays the violin a little.

Sort of a. Do not use a after sort of. See Kind of a.

Sort. Do not precede sort by these or those. See Kind.

Such. Do not follow such by who, which, or that as relatives.

Wrong: All such persons who think so will soon see their mistake.
Right: All such persons as think so will soon see their mistake.
Right: He spoke with such force that we were compelled to listen. (That is not a relative here.)

Tasty. Do not use tasty in the sense of tasteful.