If it seems that it takes longer and longer for your Mac to come up when you first turn it on, here is a quick thing you can check before you do the harder stuff.
Open System Preferences. (Apple Menu > System Preferences.)
Now click on Accounts and make sure you are in your Administrator account.
Now click on the Login Items tab.
￼This pane lists everything that is directed to open when you turn on your computer.
You might be surprised to know that a number of third party applications (applications made by companies other than Apple) just plop themselves down in this pane so that they will open every time you turn on your computer.
After a lot of experimenting I decided that it was much faster to put the apps I use the most on my Dock and open them from there than to have them automatically open while my computer is coming up. You can remove items from the login list by highlighting them and clicking on the minus button. The check boxes let you hide or view all those apps, but unless you remove them, they will all still open automatically.
If you designate more than one administrator on your machine you will need to do this for each administrator account.