A possibly infinite list of grammar mistakes you shouldn’t make, in order of when I thought of them:

1. The word ”lay” takes a direct object when used in the present tense. The word “lie” does not. Example: “I lay my book on the table.” “The book lies on the table.” “I lie in my bed.” But: When used reflexively, “lay” is appropriate, like saying “I lay myself down in the bed.”