Some people might say the microphone... or the room... or the format... but really... what matters the most are the musicians themselves. Can the musician hear themselves or the people they're playing with? If not, then you might have a problem with your recording. So what do you do?
The most expensive or best sounding microphone for an acoustic guitar won't make a lick of difference in a recording if a drummer is in the same room and playing too loud. Why? because the sound of the drums may be coming through the guitar microphone. That means that the 8 microphones you've carefully placed on the drums have been rendered useless because you won't be able to use them in the mix. Why? Because the guitar player will say, "Can you turn down the drums?" and you'll be pulling the drum microphone sound down in the mix... many times until you're using none of the drum mics.
What you're left with is the 'bleed' of the drums into the guitar... and many times, even that is too loud and the drums will sound "distant" coming through the guitar mics. The only way you can get "more guitar" would be to bring the microphone closer to the guitar (which will often take away all the value of the microphone you're using on the guitar), change microphones to a more direct microphone (often sacrificing tone), use a guitar "pickup" (which never sounds like a real acoustic guitar), put the drummer in an isolated room (and get the headphones ready to use) or record the drums as an overdub.
The more risky idea would be to ask the drummer to play softer... good luck. Most drummers get their "sound" from playing at a certain volume.
A recording engineer learns early on how to deal with these situations. The musicians often don't because they're not in the studio all the time. Trying to balance the boundaries of live playing vs live recording and still getting a great sound is an endless search. :)
If you're interested to learn more, we offer private workshops and consultation to help with your own recordings.
Meanwhile, put on your favorite music and enjoy!