One of my characters is a lancer.
Currently I have him equipped with a lance, reinforced kite shield, black armor, great helm and thick iron boots. as a backup I have a broadsword and some javelins. I use a coarser. But that's after playing for quite a while.
I started out with a boar spear and the shield you get from the constable in zendar. Make sure you have a horse with good speed, thats the first thing you'll want to upgrade. Speed affects riding damage alot.
You'll want a decent shield so you can stop any missiles, and also for those times when you get caught in the masses. Also, make sure you get something that says spear or lance. You can't use a shield with pikes, so unless you're good at dodging arrows and really know how to ride, stick with spears. A good idea for a backup weapon is something with cut or blunt damage. Make sure it is one handed so you can use your shield and also look for something with a good reach, so it will be easier to hit your foes. When it comes to armor make sure you get stuff that does both chest and leg armor, because this is generally where you'll be hit. And of course make sure you get a good pair of boots.
You'll mostly want to upgrade your horse and your spear, because these will increase your damage. As a lancer you don't need to worry as much about defense because you will be riding past your enemies.
As for tactics, ride around clockwise so you can hit guys off your right side, it's just easier that way. Also look for stragglers, because if you get caught in a group you'll probably wind up unconcious.
Hope that helps!