How to pass data from one ViewController to another ViewController

There are several ways to pass information between objects and the right way will depend on the characteristics of the application.

Using properties: Usually used when the data is passed only once, as soon as the object is allocated. I think that was the way you did it. You define the properties of the second controller and when you allocate it, modify the values of those properties:

class SecondViewController: UIViewController {

    var data: String?
}

class FirstViewController: UIViewController {

    ...
    //Utilizando segues para transição
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

        if let destinationViewController = segue.destinationViewController as? SecondViewController {
            destinationViewController.data = "foo"
        }
    }

    //Definindo as transições programaticamente
    @IBAction func openDetail(sender: UIView) {

        let destinationViewController = SecondViewController(nibName: "SecondViewController", bundle: nil)
        destinationViewController.data = "foo"
        presentViewController(destinationViewController, animated: true, completion: nil)
    }
}

Protocols: Another widely used is through protocols, as suggested by @ramaral, see