Archery development
Upgrade the archery skill first to be able to shoot two arrows at one time. This makes it easier to take out archers and weaker units.
Cavalry campaign: Break open the gates easier
Use your charge to break it open.
Defeating The Shaman
Equip Gwen with one healing item (such as Bloodring). Have Arthur kill any weak enemies. Then, have him go around the corner where he is safe and let The Shaman shoot a meteor. Remember to dodge. Finally, get behind the black circle and shoot. Because you are beyond his range, he cannot hit you. If he teleports, just let him shoot a meteor and continue from there.
Horse kick
When someone is behind you on horseback, press X to have your horse kick backwards. This can break the shields or enemies.