In order to select color for printing, two things need to occur:
1] your monitor must be calibrated for photo-retouching
2] you must use an appropriate color guide.
(If you are printing to a color laser or inkjet printer, the printer usually needs to be calibrated too.)
For monitor calibration, ideally, one would use a hardware/software calibration setup such as DataColor Spyer2Pro. This company also makes a printer calibration devise.
For general color selection, one should use printed color guides — however, one must use the correct guide for the type of printing involved. Commercial printing usually involves either spot/solid color or process/CMYK printing. (Hexachrome printing is another option.) The proper guide must be used for either printing method. You should not use a solid-color guide for selecting process colors—you will only get about a 50% accurate-match rate. And, you cannot use a process-color guide for selecting spot colors. Use the proper guide for the method of printing! In case you do need to create a process color from a solid color, Pantone makes a solid-to-process guide called Pantone Color Bridge. This guide has the CMYK breakdowns provided by Pantone.
For solid colors, virtually every printer uses Pantone solid colors, however the Pantone company also makes process-color guides*. The solid-color guides come on different paper stocks to match the type of paper you are using (coated, uncoated, and matte); the process and Bridge guides come in coated and uncoated versions.
*When most people say they are using a Pantone color, they usually mean they are using a Pantone solid color. I avoid saying simply "Pantone color" as it is akin to say I use "Adobe software"; it does not give enough information.
A note of caution about converting solid colors to process: software companies are required by Pantone to provide the latest CMYK breakdowns at time of the software release. However, some of the breakdown numbers are adjusted and refined by Pantone periodically, so converted solid colors from older files may not match the numbers of new files. It would be best to pick one set of the CMYK numbers and manually control the conversion.
If you are printing to a commerical press using a color-managed workflow with Adobe software—or are printing to a laser printer for final output—you might want to leave the solid colors as solid, rather than converting to process. When set up correctly, Adobe software* allows the use of LAB mode for optimum conversion to process. Laser printers often have their own optimized look-up tables for converting colors, which are often closer than Pantone's conversion. (Laser printers use toner (rather than ink), and print slower than a printing press, so sometimes they can get closer to the original solid color than a commercial printer can.
**Photoshop uses LAB conversion by default; InDesign can use LAB conversion via the Ink Manager; Illustrator has the LAB option in the Swatches pop-out menu.
If you do not have any guides, you only have a single spot-color guide, or your guides are very old — I recommend the package called the Pantone Essentials kit. It contains:
3 solid color guides (on coated, uncoated, and matte paper)
2 process color guides (on coated and uncoated paper)
1 Bridge solid-to-process conversion guide (coated only)
1 zip-up container to protect the guides
This kit retails for $299, buy I have seen it via mail order for $225. For an extra $50, you can get the kit plus pastel and metallic ink guides.
These guides are available separately too, but the best buy is the above kit. For example, the two process color guides can be purchased for $99 retail and the Bridge coated for $119 retail, so it does not take too many guides to make the kit a better purchase.
These guides are not perfect, since your paper quality and press quality may differ from the ones Pantone uses, but I cannot recommend these color guides strongly enough. All the guides are built into graphics software since 1990.