My Macbook Pro is running slowly and Safari keeps locking up. What can I do to fix it?

My Macbook Pro has been running slowly for several weeks. Safari keeps locking up and I have to Force Quit. It is very frustrating because it has always worked so well. My software is all up to date and I'm not using anything big - normally just Safari, Word, Excel or Powerpoint. Is there something I can do to clean it up or fix it?

Thanks!