Your deck needs a bit more field control.
Guttersnipe will help you a lot with an Izzet deck. What you want are things like
Shock and Turn//Burn.
Electrolyze is a good one too. You'll want
Goblin Electromancer too, to reduce the costs. Ultimately, if you use
Guttersnipe's ability to kill your opponent, and use things like
Chandra's Fury to boost that up, you'll be fine. Because your deck will mostly be running Instants/Sorceries then, stuff like
Cancel and
Dissolve will be necessary to keep your opponent's field clean. They'll also activate
Guttersnipe.
Chandra's Phoenix is also a pretty good card for in Izzet decks.