Here are some tips to make your mac boot faster:

Rotate your logs

open terminal > type:

sudo periodic daily weekly monthly

this command runs the log rotate scripts, etc

Repair disk permissions

applications > utilities > disk utility > repair permissions
this command repairs disk permissions, this will fix most startup issues

Spotlight indexing

open terminal > type:

sudo mdutil -i on / && sudo mdutil -E /

this command makes sure spotlight indexing is on and erases your spotlight databases, it will then rebuild them.
if you want to turn off spotlight completely then do
open terminal > type:

sudo mdutil -i off /

you can set the items for spotlight to show by going to prefs > spotlight

reset PRAM

command + option + P + R when the system boots. let go after the third bong =)

verbose boot

verbose boot helps you see whats happening on your machine as it starts
open terminal > type:

sudo nvram boot-args="-v" 

the above will enable verbose boot every time your mac boots
command + v on boot will enable it once (eg for this boot only)

don’t shutdown your mac, let it sleep instead.

by not shutting down your mac after you are done, it will go to sleep mode – its much faster to awaken from sleep-mode, than it is to boot from off.

remove login items

goto system preferences > users > your user > login items

if you tick the checkbox, then the item still starts when you log in, but is hidden.
if you click the ‘-‘ button at the bottom then the item isn’t automatically started when you log in.

Get a solid state drive

an SSD (Solid state drive) is a new type of harddrive that performs much faster than a traditional magnetic harddrive. They are expensive for the capacity, so this might not be an option for you.

After you have done all of these steps, then your mac should be nice and healthy and should boot in a few seconds (especially if you have an SSD)

Sources: Apple Support