Does your Mac seem to get slower and slower over time the more you use it? I bet it does.
There is a simple thing you can do at least once a month to help keep your Mac running fast.
First, quit all your open programs.
Then go to your home folder. Your home folder is the one indicated by the little house icon in your sidebar. it can also be found in /Users/ and has your username on it.
Inside your home folder open Library. DO NOT confuse this Library folder with others that are found in various parts of the system. The one inside your home folder is the only one you need to focus on.
Inside your Library folder you will find a folder called Caches. Drag the Caches folder to the trash and empty the trash. Restart your computer for good measure.
Most people are aware of web cache or "Temporary Internet files". The purpose of these are to make web pages load a little quicker the next time you visit a website. After using your web browser over a period of time, you tend to visit a plethora of websites and as such, your browser has to remember a lot of cache files. The more caches files it creates, the more it has to remember and after a while it just gets super slow. You can actually have too much of a good thing. Within your web browser there is usually a quick way to clear it's cache and things speed up again within your browser.
The problem is that there are other kinds of cache that many other programs and system processes create and use. Those other programs and processes don't have built-in methods of clearing the excess cache. Luckily for you, the majority of them (including your web browser) do store their cache files within your home folder/Library/Caches folder. When you delete that folder, you're essentially refreshing all those programs and processes.
The frequency at which you should delete your Caches folder will depend on how much you use your computer and what programs you use. I, personally, use my computer a LOT every day, so I end up deleting that folder once a week to keep things humming along. If you aren't the poweruser that I am, then you could do it less frequently. I'd suggest doing it at least once a month though. You should notice at least a little improvement if you stick with it. It's a good habit to have.
Something else that will help is to make sure you still have plenty of hard drive space available. If you Get Info on your hard drive and it says there is less than 1 Gigabyte of space available, you need to clear up space immediately. The operating system uses free space to handle the tasks it does and if the free space gets under 1 GB there WILL be problems.
I recommend a program called Disk Inventory X to find out what is taking up the space on your hard drive. Maybe you have an old iDVD project you forgot about or maybe you've imported a few thousand too many songs into iTunes...