Depends on your acoustic and your mic to some degree. Does your guitar have pick-up at all? What kind of mic are you using, dynamic or condenser? Pick or finger style?
As a general rule of thumb either (a) point the mic at the 12th - 14th fret, place your mic 12 - 18 inches (30 - 45 cm) away from the instrument, (experiment til you find something "nice"); or (b) another tip I found at Produce like a pro, who made a video on recording acoustic guitars where he points a dynamic mic at the bout near the "shoulders", pointing away from the sound hole.
Once you have the sound "in the box", a bit of compression (to control signal dynamics) and a bit of e.q.(roll off (cut) low frequencies (I aim to cut anywhere between 80 - 100 Hz), cut the muddiness from the mid - range (anything between 350hz - 600hz (find what suits)). Then I attack errant high frequencies. Generally cut frequencies in e.q. and do not boost. If you haven't read anything on gain staging I suggest you do. Again, youtube has videos on the subject. However - rule of thumb only cut by 2 - 3 dB at a time.
Gain staging - I generally input my guitars to peak at about -24 dB for the noisiest part. At -24 dB you still have another 24 dB to play with when e.q.'in' or compressing before you're clipping. You can add reverb here if you choose but use it sparingly and try to use delays as an alternative if you can.
If you have an electro-acoustic - everything above is still relevant. However, you have the option to send the pick- up signal via an fx unit or an amp before hitting your audio unit.
Personally, I use a Fishman Blend in my guitar, an SM57 at either point (a) or (b) as (described above) and place a condenser (MXL 770) a bit further away for room sound. This gives me three tracks, which is overkill to a certain extent but gives sonic options that e.q. and compression just can't do. Its not the gear - it's the ear that is more important.
Last thing to remind you of - no matter what is happening, make sure you're enjoying the playing of the guitar while you're recording! I can't stress enough how important this part of the equation is!!!!! (maybe I can with bold text?). Regardless of kit and placement of said kit and settings on said kit, enjoy it.
