Consult music store employees specializing in live sound. Ask about different types of live sound mixing equipment and which are best for indoor and outdoor venues. Ask which are most appropriate for your particular genre of music.
Contact a university with programs concentrating on live sound. There are universities all over country that teach students such courses, such as Full Sail University and Cogswell California Audio Engineering Technology College. Speak with an instructor or instructor's assistant and ask what types of mixing equipment are best.
Talk to roadies. These techs are a repository of knowledge of live sound mixing. Because they set up and use the equipment on a regular basis, they can possess an intimate knowledge of sound engineering. Also talk to live sound engineers.