There are things you can do to help, but the way you approach it depends on several things.
For example, are your pages static html, or are they dynamically generated?
Do you use any “CMS” style software to manage/create dynamic pages (WordPress, Joomla, etc.), and, if so, what caching options are available to you with that software?
We could advise better if you provided answers to the above questions, as well a the url of your site
Understand that irrespective of what you do, results are likely to vary to some degree among your visitors depending upon ISP caching (AOL is notorious for caching pages longer than they should), and their browsers’ settings.