Instead, the player should be patient and look to the other rulers of Europe to prepare for future expansion. The player should be careful though, since taking too much territory will drive up his threat quickly and allow his many enemies to form a strong defensive pact. The player can then attack either Alfonso's brother or the Muslim ruler either way, he should be able to seize for himself a good chunk of territory. The best strategy is for the player to wait until his brothers have been attacked or are attacking a large Muslim realm and then let both sides weaken their forces.
These realms can be tricky though because the holy war casus belli allows the Muslim realms to band together and perhaps combat the combined forces of even all three kingdoms. If fighting Alfonso's brothers is out of the picture, the player can instead concentrate on the Muslim realms in southern Spain. Failing that, Alfonso and his heir will have strong claims to his brother's kingdoms. Killing them both is difficult, but if the player succeeds, he will control by far the most powerful Kingdoms in Spain. The Kings of Castile and Galicia are Alfonso's brothers and therefore Alfonso is in the direct line of succession for their kingdoms. The easiest path to expansion for the player at the beginning of the 1066 start date is not conquest or crusading, but instead the killing of only two men.