When a red cross appears on an enemy tile when you are attacking them it indicates that your current attack is powerful enough to dispatch them. If you don't see a red cross you need to add some more swords to your chain.
Shield Tiles
Match up shield tiles even if your armour is undamaged because if you collect enough you can upgrade your armour so it has better attributes and enchantment.
Skills
Try not to forget skills you have learned as they can get you out of trouble later on in the game and using a Skill doesn't end your turn.
