As are probably aware amplifying acousitc guitar live is fraught with problems.
The main issues are feedback and avoiding amplifiying extraneous noise.
The "best" approach will depend on the circumstances in which you are operating, ie are you playing with a band, how much sound is going through the PA etc.
The best sound is probably achieved by micing the guitar, and condenser mic/s are usually employed for this. However, if you playing with a band it then you will have real trouble with the mic picking up other instuments, especially drums. If you playing alone, or with other fairly quiet instuments, then this appraoch is worth considering.
The other approach would be to use a pickup in the guitar. These will either be of the under saddle type (which will require fitting into the guitar) or the sound hole type . Both are sonically a compromise, however they are a much easier than micing, and with careful eq can sound great, especially in the context of a full band.
For best results you will also need to eq the sound carefully.
As with all instruments it is adviseable to roll off as much bass as you can get away with. A slight treble lift can add a bit of sparkle. Also if you are using a pickup rather than micing, then there is often a fairly nasty frequency between 1-2 kHz which if you cut gives a much more natural sound. You will need a parametric to sweep through this region to find it. I sweep a small boost to find the troublesome frequency (you'll know when you find it!) and then cut it.
Regarding feedback, most systems have a phase invert on them, so first try to see if this makes any difference. Additionally a notch filter may also be required to zap and problematic frequencies from feeding back.
