The most common hiring mistake is hiring someone for their technical skills, regardless of their ability to work with other members of the team. Finding someone who culturally fits your company is more important than any technical genius. A cohesive team that gets along and works well together is better than a developer rock star that no one can stand working with.

If you're unfamiliar on what to look for in terms of technical skill ask questions about how they get things done. If you aren't familiar with coding, ask a current developer to join you in the interview process.

For iOS and Android developers it is great sign if they have apps out in the marketplace. Take a look at the apps already released by the developer to gain a sense of their skill and experience. This is a better indicator of their level of quality than a resume.