Check for a subject, which is the "do-er" of the action of the verb. All sentences must have a subject, such as "I" or "you" or "the pen" or "cats." Read the sentence, figure out who or what is doing the action, and add the appropriate subject.
Check for a verb. The sentences "She always the ball" and "He the meat" aren't complete and don't make much sense. If we add a main verb---"She always kicks the ball" and "He is cooking the meat"---the sentences are now complete and make sense.
Check for subject-verb agreement. For example, the sentence "I likes her" is incorrect because the verb "to like" conjugates with "I" in the form of "like" and not "likes." Some verbs are irregular and thus have irregular forms with various subjects. Consult a verb book if necessary.
Check for articles. Articles are words like "a," "an," or "the." Make sure that when "a" or "an" appears in a sentence, it's because the writer is talking about one unspecific item. Make sure that when "the" appears in a sentence, it's because the writer is talking about one unique thing. Switch articles or add articles as necessary. For example, the sentence "I fell on a floor" would be incorrect since wherever the writer was, there was just one floor. Thus the sentence should read "I fell on the floor."
Check for double negatives. Remove one negative word and replace it, if necessary, with a word that does not have a negative connotation. For example, you could fix the sentence "I don't have no money" by replacing "no" with "any." Or the sentence could read "I don't have money."
Check for run-on sentences. A run-on sentence is two or more main clauses connected by inappropriate punctuation. For example, "I love ice cream, it's so cold and creamy" is a run-on sentence since a comma cannot correctly link two independent clauses. You could use a semicolon---"I love ice cream; it's so cold and creamy"---or you could separate the clauses into two complete sentences---"I love ice cream. It's so cold and creamy."
Check for apostrophe use. People commonly confuse possessives and contractions: "Its unclear what it's purpose is" should read "It's unclear what its purpose is." "It's" is the contraction of "It is," and "its" is the possessive pronoun that shows, of course, possession.