First rule for you to remember (should you come from the UK) : drive on the right part of the road! Be especially careful when setting off from service stations or restaurants on the left side of the road.
Also, bear in mind that you may have to give priority to traffic coming from the right (priorité à droite), especially in built up aeras or when on small roads. Usually on large roads you do not give priority to the right, except on the périphérique, the highway around Paris. Those road signs will help you identify when to give priority:
You have to give priority to traffic coming from the right (eg intersection of two small roads).
You have to give priority to traffic coming from the right and from the left (eg a small road intersecting a large road).
You have priority at the next intersection (eg a road intersecting a smaller road).
You have priority at all the following intersections (eg when on a large road) untill you find :
You cease to have priority.
Roundabouts : you give priority to traffic already on the roundabout, in other words, coming from your left as you enter the roundabout.
Enjoy your driving!