Determine if you want a  DIY wireless system, or an installer based hardwired system

Analog vs. Digital

If you have older COAX wiring existing, Analog upgrade may be a good fit, otherwise an IP camera systems is the preferred choice. 

Local vs. Cloud

A Local system stores video recording on hardware located in your home and is free once you have purchased your equipment. Cloud based systems record your video off site, usually for a monthly fee.