Lightning. Do not use lightning as a verb in place of lightens.

Wrong: During the storm, it lightnings frequently.
Right: During the storm, it lightens frequently.

Like. Do not use like for as. Like is a preposition. As is a conjunction.

Wrong: He doesn't talk like he did yesterday.
Right: He doesn't talk as he did yesterday.
Right: It looks like a mahogany chair.

Lit on. Do not use lit on in the sense of met with or discovered.

Wrong: I at last lit on this plan.

Lot. Do not use lot in the sense of a great number or a great deal.

Wrong: A lot of people were there, She talks a lot.

Most. Do not use most for almost.

Wrong: I have most completed the book.
Right: I have almost completed the book.
Right: He has done the most of the work.