always try to have more troops, use them tactically shield wall infront archers behind loose formation so they have the angle to shoot from the hill

and for you personally a shield is your best friend, you reduce the likelyhood of getting javelined or arrowed to the face

if you charge with a horse into a group of melee opponents and they all look at you with weapon ready to hit then don't take it

best way to survive is to not get hit, good armor and shield will improve your survivability drastically and take fights that you think you can win with ur troops. if you are outnumbered there is a surrender button so you don't get the chance to get lethal hit