Also, do not eat at a chain restaurant (unless it's a chicago pizza chain) because there's way too much local and ethnic food available and it's sooooo good.  Take advantage of the many used and rare bookstores located all around town (often in basements of buildings).  I recommend just walking around for a few hours and poking your head in interesting stores, restaurants, and buildings.  Do this before the book comes out or after you've read it! 

The lakefront is fun to visit.  You can read your book on the beach if the weather cooperates (not likely in April). 

Enjoy the Blues and comic clubs.  There's a lot of commercial excitement around Navy Pier (if you bring kids) and Michigan Avenue (if you want to spend a gazillion dollars or just like ritzy window shopping).

Stay off of Lower Wacker once the sun goes down because that's where the trolls live 

And if you drive, make sure you bring a small fortune for parking and remember which parking garage your car is in.  Chicago's a big place and many of the parking garages look the same.  Not that I've ever forgotten where I parked and walked around for 2 hours in the middle of the night looking for my darned car    Trust me, those homeless shelters start to look inviting after a while!