I like building my mana base early, but if I am using creatures heavily, I like to use my full action as much as possible to summon creatures each turn. I usually lay out my spell book for my first three or four turns as I love the consistency you can have with this game in preparing your board. Having  a  plan and foundation early really helps the middle and late game. It's also fun to throw out a
small flyer or fast creature early to start disrupting the other mages plans and if you can incorporate this into your opening moves its great to see spells from the other Mage wasted on things that are not important to your overall strategy.