Tiamat is a slow starter, with her one needing to be levelled to max for full potential. Although that doesn't mean you can't catch a few people out who underestimate the mother of the monster's early poke. Taking the jump at level 2 keeps you relatively safe in lane and offers an out during the junglers pathing through mid.

Try to avoid stance switching to clear waves as this is very mana consuming and has a long cooldown. During the early levels, stance switch should be utilised as an escape or to confirm a kill.

Levelling the ult later allows you to steadily build momentum with Tiamat, letting her main damaging abilities become stronger quicker.

After recent buffs, Tiamat's tornado serves as a fairly decent disrupt in fights, although keep an eye out for stone of Gaia.

The minotaur in combination with a flying form 2 on top of you are great ways to try and shake enemy gods stuck to you.

After soul gem, you want to get Bumba's as soon as you hit 20. With Bumba's hammer, you will be able to cycle through your abilities much faster and thus be more agile and put out more damage.

I hope this build serves you well as it has with me. Obviously, always build for the situation, healing needs anti heal etc. But with the current state of mage starters, I find Bumba's hammer to be a good go to for most mid-laners but it really shines on the goddess of the salt sea as your late game damage potential becomes insane.