Use Activity Monitor to keep an eye on your disk use and memory use. You may hear different figures, but I like to see my free disk and free memory above 25%. Sometimes all it takes is a Restart. Try to minimize the number of browser windows you have open at once. Quit unused applications.
Many of us in this discussion area like to use OnyX periodically. It clears caches and repairs permissions, etc. You can download it from this site. Be sure to download the one for the OS version you are using. There is a script called Automation within OnyX that allows you to start it and come back later when it's done with several actions.