All great advice. Couple small comments....

As the English you can get Frydmen quite quickly in early - they are sturdy spears, equivalent to Feudal Sgts and a lot better than plain spearmen. (Billmen and longbows are available in High, and the build requirments are greater.)

Don't neglect militia sgts - they can be deadly against most everything, though their moral isn't the greatest. (They are decent polarms - early versions of halbs/billmen.)

I've found that the half-square formation can be quite good when you have a foot army defending against a mounted one. Mix in a few spears, archers, and militia sgts. Set it up around a copse of woods if you can - have the woods to the backs of your men so your archers can fire out at oncoming enemy, and your soldiers can retreat backwards into the woods if they are charged by the cav (cav fight poorly in woods) or if you start getting rained with arrows. A little elevation is a plus. Don't let the enemy lure you out of your position too early, or they will slaughter you in the open. Often the enemy will attack one side of your square; then you can shift the units from the free side over if things start getting hairy.

(The easiest way to set up is to select the half-square formation, select and then group all your units, then click on the place where you want them to be. Now if you position your cursor and alt-click you can rotate the whole formation to get it exactly where you want it.)