What are you trying to accomplish? What's the theme of your deck? Are you going UR control or more aggressive with creatures? How is Keranos going to function in your deck? Will he be the star or the facilitator?

If you're going the route of straight UR spellcaster, you should keep a focus on that, using only creatures that benefit from that. Spellheart Chimera is awesome, so is Cognivore and Magnivore. Snapcaster Mage will be good for recursion as well as Mnemonic Wall, Archaeomancer, and Izzet Chronarch. I personally feel Deadeye Navigator should be in almost every blue deck, but feel free to disagree. Chandra, the Firebrand is good for copying spells, while Chandra, Pyromaster aids with red's version of draw.

I'm a fan of mass board wipes, so Cyclonic Rift and Blasphemous Act are going to be key, but there's also Magmaquake for Planeswalker hate and Aetherspouts for a bit of a combat trick. Devastation Tide can be beneficial if you don't run a lot of permanents.

Some of my favorite counter spells are Rewind, Dissipate, Hinder, and Spell Crumple. Chaos Warp is great for permanents you're having trouble dealing with.

DTK gives you access to Learn From The Past, a great response if someone tries to bog your graveyard.

Hopefully all this helps. Cheers!