Getting my MacBook Pro ready for Video Editing, what to upgrade?

Firstly what software will you be using? Different software may require different hardware. RAM is never a bad thing to constantly upgrade. Most video editing software is reliant on RAM. I work as a VFX Artist and Compositor and from time to time as an Editor. My home machine where much of my work is done is a 27" i7 iMac. For this machine I have 16GB of RAM. The software I mainly use are Adobe After Effects, Adobe Premiere, Adobe Photoshop, Avid Media Composer 6, Apple Final Cut Pro (7 & X), The Foundry's Nuke, Autodesk 3DS Max and Autodesk Maya. I also use REDCINE-X when I working with a RED workflow. All of these applications are heavily reliant on RAM. A fast HDD/SSD wouldn't go a miss either! For the 3D applications (3DS Max and Maya) the GPU is also relevant but nowadays these apps are more reliant on RAM.

I would upgrade the hard drive. A solid state drive would be excellent since during editing the computer will constantly be fetching data and writing data. A solid state drive would help not only that but would also improve boot times.

ok solid state will make your computer fast but on the down side is cost/volume which in this case is would not be bad for internal, sense FCX does not take nearly what FCP 7 did. I would recommend ram upgrade up to 16 gb as that will help considerably with not only render but export, and btw a 15" MBP is actually a great computer for video editing considering your setup. it has the power and portability for editing on the go type thing,

i would get a decent pair of headphones over the head for when you are editing nothing to fancy but good sound and if it blocks out the background all the better, i can't think of anything else

btw a 7200 rpm hdd probably won't show a major difference i would say either ssd or 16 gb ram as a nice upgrade that should should see performance wise