One of the biggest stumbling blocks for first-time recordists is capturing acoustic guitars.
There are many ways to mic these instruments, and also many ways to go astray. Good mic preamps and good mics are important, but having those mics in the right places is the most important.
Here is a "default" recipe for acoustic guitar. There's an ideal situation: great room, great instrument and great player. Probably not all of these show up at the same time, but let's at least assume no one is singing while playing the guitar — that would be a whole different article.