Hearthpwn

Strategy:

Play your Academic Espionage, play your Spirit of the Shark, Prince Keleseth then Shadowstep play the keleseth again, all your minions have 4+/4+.

Now this is minimum, what I like to do is double Espionage, double shadowstep so all minions have 6+/6+. 

Mulligan:

You don't want to trade in your espionage, keleseth or shadowstep because theres only 1 keleseth in your deck and there is no spell draw. However, depending on class, you might want to keep a taunt minion in your opening hand.

Other Strats:

You can play your espionage(s) earlier in the game so that if things start slowing down you'll still have some cards to play. However keep in mind, that if there aren't too many in deck then keleseth becomes pretty futile. I'd suggest if your in a tricky situation to play one and at least hold on to the other.

Tips:

You can do the combo in one turn, but if you have two spirit of the shark's in hand, don't be afraid to throw it on board so you don't need to use a preparation or two.

Sprint can be used to get your combo cards, however, I think it's better off used after you've keleseth'd to get you 1 cost cards.

If you have an extra Spirit of the Shark, hold onto it incase you get something with a good battlecry.