Check for any software updates that may be available for the version of OS X your computer is running on. Often, software updates fix bugs and glitches that could be slowing your computer down. Check the boxes next to each app and click the minus button at the bottom of the window to remove them. In this list, you'll see all the items that start up with your computer. You can see exactly which apps are programmed to launch on start by clicking the Apple icon and navigating to System Preferences > Users and Groups >Login Items.
If you have a bunch of different programs set to launch when you turn on your computer, it's going to take a while for your Mac to boot up.
