If you're coming under heavy fire in the game hold down the shield icon so that you can take a battering.
Keep in mind that the light attack doesn't do much damage but it is fast.
On the other hand the heavy attack is slower, does more damage, but leaves you more exposed for a counter-attack.
You can remove active runes from the bottom left of the screen and replace them with the runes listed in the main rune area.
You'll receive new runes as you progress through the story. To activate them and add them to your inventory stand in the shimmering blue circle and hold down the shield icon until the meter has fully charged up.
Purple gems that drop from thei enemy corpses will help you upgrade the power of your runes.
Ssmashing any objects and vases that are lying around often bring out a handful of these gems as well.