If you are playing the English in the Early Period you can sometimes grab Navarre if you are quick. It not only provides upgraded weapons for your troops, but also denies them to a rival (usually Spain or the Almohads). I tend to ally with the French early in the game and concentrate on conquering the British Isles and setting up trade routes. I usually wait until the 1130s/40s before attacking the French, although it is worth having a large army on the continent before then so you can capitalise on any rebellions. When fighting the French my main targets are Brittany and Flanders as these have the greatest strategic significance. A third target to conquer if the opportunity presents itself is Toulose, giving you a Mediteranean trading port and a springboard for a later invasion of Aragon.