I normally like to put an inquisitor or 2 or 3 really into the provinces ahead of what will be my likely crusade path to pump up the zeal before I even get there.
An extra 4-5% zeal really can make a huge difference.
This is even more important in the middle high to late periods were generally zeal is dropping through europe.

This also has the added benefit of giving you the information as to which provinces that you will have a choice of travelling through have the best zeal, the highest standing armies and the best upgrades to get the most numbers and best troop types for your crusade.