Please excuse Sarah for being absent. She was sick and I had her shot. My son is under doctors care and should not take P.M. Please execute him. Each pronoun agrees with their antecedent. Just between you and I, case is important.
Verbs has to agree with their subjects.
Watch out for irregular verbs which has creep into our language. Don't use no double negatives. A writer musn't shift your point of view. When dangling, don't use participles. Join clauses good, like a conjunction should.