Runescape, How to PK using Mage/Range to my advantage?

Well I've decided on becoming a Mage/Range hybrid (50 Mage, 40 range). But the problem is I don't know how to use it? With melee you just attack, range you just shoot arrows and with Mage you just fire spells. What do I do? Just randomly swap between Mage and range when I feel like it? Help people! Every answer is useful!