Generally the left lane is the "fast" lane and the far right the "slow" lane, but there's not really a steadfast rule about it.
Allow extra time whenever your trip involves I-4, there always seems to be something going on to tie up traffic around the general Orlando area, whether it be traffic or an accident.
Definitely be mindful of the speed limits, as cops in this country (or at least MY part of the country) love to tag tourists or out-of-town drivers.
If you're planning on driving to the Disney parks, beware. Some people can be awful pushy and reckless when there's thousands trying to exit all at once.
But rest assured, driving around Disney is definitely not a problem at all, everything is well signed and not too easy to get lost. And also, keep in mind most hotel and resort guest services areas have ready made business cards with directions to popular destinations on and off property, so rather than relying solely on maps and your own navigational skills, do ask there for help ahead of time.
Keep the phone # of your resort programmed in a cell phone (or in the car, if you don't have one) just in the odd event that you find yourself misplaced.
And most importantly...have fun!