1. Love story 2.Tom's plan 3.Tomorrow meeting

1. That film is a story of love/ a love story. [Both are all right. It is a choice related to emphasis of the writer.] 2. Tom has an excellent plan. [Avoid the apostrophe, and it is awkward to say "the plan of Tom".] 3. The meeting tomorrow has been cancelled. About the apostrophe, it is a confusing mark and often misused. Avoiding it is a sign of good writing.