using HA's try to pester the flanks as much as possible, get some units to give chase and then crush them when apart from the main force

when they just don't budge or your HA's start getting under fire from their archers I usually go with the small wedge/large flank maneuver. Sometimes you have to tweak a bit depending on the troops you have/facing but it's basically like this:

Advance with a small wedge with a reasonably strong unit at the front, not something whimpy. THen have that flanked and diagonally spaced backwards from it and advance on the enemy. This will ensure that your units aren't outflanked as quickly. Then have one or two units march around the enemie's flanks. Just having one on the enemie's weakest flank works the best as after slaughtering their weakest troops you can sweep into their rear. This has worked a number of times for me but it has failed obviously when I should've used a different tactic. Basically you're just trying to get them to concentrate on your main force in the center first, so those units should be pretty hardy so they can stand fast and wait; having your general in teh center works well for giving extra Moral.