Compression can be used to make LOUD sounds quieter and

in the process also makes quiet sounds LOUDER (as well as making the noise floor louder)

compression can then be used to create the sound that you want

A decent Mic is also usually necessary.

The most popular pro small diaphragm condenser mic being the Neumann KLM184

(which isn't cheap).

Often used with a large diaphram condenser mic such as a Neumann U87

(although not always necessisary)

From what i have read, some pro engineers will use a large Diaghram condenser such as a Neumann U87 combined with a dynamic microphone such as a Sure 57, which gives the recording an extra set of complimentary frequencies to combine with the more neautral signal from the U87.

Although I would say that some still get great recordings from the Neumann KLM184.

[br]If these mic's are too expensive for you at the mo, then perhaps consider cheaper alternatives such as Rode NT1 and AKG P170s, or blue lines.

as for compressors, UAD make a good range of compressors

which give choices for all sorts of uses and tastes

in order to use their emulations however, you would have to invest in one of their interfaces and perhaps also some UAD DSP hardware. Which i am afraid doesn't come cheap.

For just acoustic guitar recordings, you would likely have enough DSP power built into one of their apollo interfaces, as long as you don't want to use too many plug ins.

Their reverb plug ins, which are absolutely awesome, are really DSP power hungry.

There is nothing stopping you recording the guitar using a pre amp emulation plus compressor, bouncing that down and then adding reverb and eq the second time around?