I'm at turn... 87, I think, in my Spanish campaign right now. Thus far, I've knocked the Moops (No, it clearly says "The Moops!"), Portugal, and France out of the game, in that order, and am working on taking out Sicily and Milan, which should be semi-easy, if I hadn't taken over half of Egypt early in the game in a crusade, and (to save cash) razed all the buildings in the cities I took before gifting them to Milan. Anyway...

I could go through how I went about it, but all I really have to say is this: every army should be half jinetes, at least until you can start getting KOT and chivalric knights.I have a tactic that pretty much works without fail, as long as you don't choose a wooded area, and the armies are closely enough matched that the enemy will march on you:

1) Set up your infantry in a straight line, general dead center in the back, with any mailed/feudal knights or missile infantry on the flanks. You want them as far back as the map will allow, in order to tire out the enemy as much as possible. These units will NOT move until the enemy general(s) are dead, and half their units are routed.

2) Set up your jinetes in single file formation, off to whatever side the enemy won't be coming from, preferably behind a hill or a stand of trees.

3) Start battle.

4) Walk your jinetes around the enemy, and pull in straight from behind. Turn off skirmish mode, auto-fire, and cantabrian circle. Individually have each unit attack the general unit. Since you're nailing them from behind, they usually won't turn around at all, and usually will be dead before they even have a chance to rout (and, even if they did, they'd have to run through all of your jinetes to begin with). Now start pounding away at whatever units look the strongest with your jinetes, since they're all going for your "heavy" units (the infantry and mailed knights and general), they usually won't turn around.

5.1) If they turn around, charge right into them, as long as they dont have spears. Go two on one if possible, and have one group swing around from the side.

5.2) If they don't turn around, keep killing until you run out of javelins. Then pull your units back a bit, and charge. But don't aim at units... just set all of your jinetes to run straight back at your general, through the the enemy units (who should be fairly close to your infantry line now). Now have your heavy cavalry swoop oin from the sides, while your infantry marches headon.

Works every time, at least for me.