Before starting this, you should make sure your EFI firmware is up to date. Follow this Apple TN EFI & SMC firmware updates for Intel-based Macs
If you are just replacing your current HD for the SSD drive:
You first need to prep both your SSD and an external FireWire or USB HD or a USB Thumb drive as a bootable drive (you'll use this drive to do the file transfer). Using the Startup Disk Control panel make sure your external HD your SSD is able to boot up your system. Once you get to this point you know your SSD is ready (reset your startup back to the external HD) then using CarbonCopy or other cloner copy over your OS & data from your old HD to your SSD. Again using Startup Disk select your SSD as the booting disk again making sure everything is working. Only at this point should you take your current HD out and put the new drive SSD in.
Clearly you can't fit all of your stuff over if you have more than what your SSD can hold. In fact I wouldn't use all of the space at all. You should leave at least 1/3 of the storage as free space (not to be used). Using an external disc make a full copy of your stuff and trim back what you have on your HD to what you will have on your SSD. I would recommend running Disk Utility using your external disk as the booting drive to test out and repair as needed your internal HD. Also make sure you repair the permissions too.
You may want to think about swapping out the optical drive using the dual drive kit. If you can't trim things down. Maybe even setting up the two drives as a Fusion drive.