Assuming by 'missed approach' you mean a Go-Around and missed approach there are a lot of reasons why you might conduct a missed approach:
Unstable on the approach (too high, too low, too fast, not configured correctly)
ATC mandated instruction
Blocked runway
Not visual with required minima at decision height
The approach 'doesn't feel right' (woolly that one!
)
Deep landing.
Bounce.
A malfunction that mandates an automatic go around (normally associated with low vis ops but not necessarily, etc. Gear malfunction/flap/slat malfunctions, anything that might change the landing performance from that which was briefed!)
Once the decision has been made then the procedure is pretty routine from my point of view. Initiate the go-around calling for any flap changes, power up, pitch up, gear up when climbing. Climb to the missed approach altitude, accelerate, clean up and follow the lateral and vertical profiles of the procedure. In many places, Zurich for example, the GA procedure is pretty complex both vertically and laterally and really needs to be properly briefed not only as to why you would fly it but also how.
Hope that helps.
