Macros

One of the biggest barriers I face on my casters and hunter is spellcasting/shooting efficiency. As much as I wish they would, haste potions won't help me push buttons any faster. One thing that will, though, is macros.
A macro is simply a command bound to a key or a mouseover. For instance, one of my favorites is a simple targeting macro. If I'm single-target dpsing, for instance, I might have a macro that says /assist . You have to put the tank's name in each time, but it does make it easier to acquire your target faster. If you are looking around for a target and trying to click it, that's time you aren't doing damage, and that affects dps.
A simple shackling or trapping macro that works well:
/cast [target=focus] Shackle Undead or /cast [target=focus] Freezing Trap
/assist
To set the focus, simply target your target and type /focus. This can be easily done before the pull. When I was playing the hunter in Kara, I had three different trapping macros for the Moroes fight because the tank I was assisting changed.
You can also set a macro for spell rotations. I have corruption and shadow bolt bound to the same key because I cast them in sequence, same with unstable affliction and immolate. The macro for this is /castsequence Unstable Affliction, Immolate. I press it once for Unstable Affliction, then again for Immolate. Instead of making my opening cast sequence 1,6,2,3,4,5,7; with two macros it becomes 1,1,2,3,3,4,5 and then can spam 6 (shadow bolt) until it is time to refresh.
A very helpful article I've found is http://www.wowwiki.com/Making_a_macro.
Happy raiding!