I have hired hundreds of people during the course of my career.  In my experience, the most effective way to make solid hires consistently is to a) conduct an analysis of the candidates history of accomplishment and b)evaluate brains.

I understand you are currently seeking summer interns, no problem. Today, young people that are proven achievers have much to examine:

1)  Projects they've built or been a part of--just because they were curious if they could do it.

2)  What are they passionate about:  who have they read/studied in the area?

3)  Are they aware of market leaders in your sector and can they discuss what they believe is right/wrong in their model.

4)  Extra-Curricular's (speaks to buy-in of culture)

5)  How do they define providing value/work ethic?

The above represent top 5.  Be certain that when you find a candidate you'd like to hire that you can articulate the value proposition you offer to them. Be prepared to demonstrate how being a part of your team will benefit them.  Don't bullshit, anybody smart enough that you want to hire can smell it a mile away.  Be Good.  Absolute best of luck.