Gems
Complete the optional achievements to get gold and gem rewards. Gems are spent when leveling up your stats and spells. Gems can be spent to increase your base stats, which will modify your mana regeneration rate, armor rating, and your maximum health. Consider upgrading your base stats first before making additional magic spells available.
Magic
The green absorption shield is your starting magic ability. When activated, it lasts a few seconds and will complete absorb any incoming damage. You can use that spell immediately if you hit a green magic orb, but it also recharges by itself. The amount of its charge is displayed on the bar on the right side. You can cast it after it has been fully charged. After gaining new magic spells, "equip" them on your spell list to make one your default spell when your mana is fully charged. Consider doing this with "Heal", as it will help save you in tough situations.
Weapons
Consider continue using your bow. By tapping accurately it can be used to kill very distant enemies before they have a chance to do damage to you. Make sure to use stronger arrows for targets such as armored enemies on horses. If you are forced to fight in close-quarters, try to get the perfect sword angle to decapitate your enemy. It will kill any enemy, regardless of their armor.