As a crusty mechanic once told me as I pulled out of a rental lot at Belfast Intl., "the lights on the cars directly in front of you are supposed to be red; if they are white, you are in a bit of trouble."
Seriously, one tip to remember in order to keep yourself inside your proper lane without weaving around, is to sight the centre front point of the car's bonnet ("hood" along the white line at the outer edge of your lane. This rule works regardless of which side the driver is sitting on.
Here are the differences I've noticed between UK driving and US driving, apart from the obvious:
Motorways are known as "interstates" in Florida. (They are known as freeways in some other parts of the US, but that's not a term often used in Florida.) These roads may or may not have a toll levied on them; many of the motorways leading out of the Orlando airport and/or into WDW have tolls on some part of their length. Your map will indicate toll roads by color; check the legend.
On motorways, the "slow" lane is the righthand lane. If traffic is sparse, try to stay in the righthand lane. In situations where traffic is heavy, it is usually acceptable to fill up all lanes, and in a situation where traffic is heavy, the left lane is going to be more comfortable for you, anyway. Just remember that you will probably have to get into the right lane to leave the motorway.
As we don't have many roundabouts (at least not in Florida), you need to familiarise yourself with intersections and exits. Exits (found on motorways) are akin to the spokes of a roundabout; just know which one you want, and follow the sign for it when you see it. Most exits veer to the right on US roads, but some do go left. At intersections of surface roads, follow the light signals if there are light signals; your FL driver guide will explain those. If the intersection has stop signs on all 4 entry-points, it is a 4-way stop. The driver guide will explain right-of-way at 4-way stops. However, if you are not sure if you have right of way or not, and the drivers seem to be hesitating, best to wave your hand (inside your car, no need to get out!) and indicate that the other car should go first; they will think you are just being nice.
When the motorway crosses over another road in the manner of a bridge, it is not called a flyover; it is called an overpass.
Americans measure short driving distances in blocks, and if you ask directions, they are likely to mention them. A "block" is the interval between one cross street and the next. Some blocks may be longer than others; the ones on I-drive are especially long; sometimes as much as half a mile. So if someone tells you to "go 3 blocks and make a right" they are telling you to proceed to the third-next cross street and turn right on that street.
In commercial districts where streets are laid out in a grid, if you go too far and miss an address, you can often "make the block" to get back without having to find some place to turn the car around. "Making the block" means making 4 sequential same-direction turns at each street you come to (most commonly, right turns). This will take you right round the perimeter of one block, so that you can re-trace and correct your mistake. If you need to go back further than one block, that is often possible. This does not work as well in residential districts, especially newer ones, where streets are seldom laid on a grid.
Also, one-way streets: If a street you wish to turn on is marked one-way going in the direction opposite that you wish to go, don't turn the wrong way! Instead, proceed to the next cross-street; it should either be 2-way, or be one-way in the opposite direction.
Generally, driving in Florida is very easy compared with most parts of the UK, especially around Orlando. The city is new, and the streets are wide and laid out pretty clearly. If you are used to driving a manual-transmission car at home, don't be surprised if you find yourself whacking your left hand against the door of the car for awhile; I always do that in the UK, expecting the gear stick to be opposite where it really is.
we're you thinking about driving to the US from the UK? 
