Audio Systems: wireless microphone, wireless microphone, voice grade

Question
i want to purchase good sound quality and best signal connection wireless microphone so explain me what thing are keep in mind?
explain in simple language.

Answer
Frequency band (that is legal for your country)
Distance range (most of them are for a few meters)
Receiver (FM radio or special made)
Sound quality (voice grade for annunciation or music for theatre arts and stage production)
Battery type and hours of use on one charge
Dynamic range

http://cdn.shure.com/publication/upload/438/us_pro_intro_to_wireless_ea.pdf

Above may be good tutorial for you.