At roundabouts, junctions, or coming out of petrol stations remember 'keep your bum in the gutter' and you'll keep to the right side of the road!
Generally routes are better signposted than in England - easier to follow somehow. The major signs indicate the next large town or city on that route - so you may get a sign just south of Paris indicating 'Marseille' which is hundreds of miles away. If your destination is south of Paris, and on the way to Marseille then you just take that road until you see the sign for 'wherever you're going'! Sounds complicated but it's not, honest. Autoroute signs are always in blue - N road signs are in green and if there are two together indicating the same destination it means you have a choice of the autoroute (if it says peage then it means it's a toll road) or N road.
Keep absolutely to speed limits, and always STOP at STOP signs - there may be police on the junction watching for those who just slow down. People coming the other way will often flash their lights - this indicates police or a radar trap ahead! Don't drive too far - there are loads more places to just pull in for a stop, both on the autoroutes and often on cross-country roads. Take advantage. It's a big country and people often try to do over-ambitious mileage in one day.
Even if you have Satnav buy a paper map - the Michelin book is good because it's manageable, and detailed enough for all the minor roads.
Slow down through towns and villages - at the entrance to each village on country routes there is always a sign giving the name of the village. Beyond that sign the speed limit is always lower (often 20 or 30 kph) through the village, until you see another sign with a cross through it - that indicates that the lower limit no longer applies.