1. Use MacJanitor
2. Delete files from User>Library>Cache
3. Use iDefrag
4. Shutdown and restart when it's running slow.
5. Use Disk Warrior
6. Repair permissions
There seems to be a lot of disagreement about whether or not defragging a mac is of any use. From my personal experience, especially if you're dealing with a lot of large video or image files for editing, it makes a HUGE difference to the speed after a defrag, and I know of many other people who have experienced the same difference as well. At the end of the day, it's whatever works best for you.