What Acoustic Guitar Strings Should I Buy?

This is a very common question for beginning guitar players, as the choices can be overwhelming. Not only are there dozens of different brands, but there a different gauges, different string materials, and all have different purposes and characteristics. So, let's address a few common questions that will hopefully clear up some of the confusion

My guitar came with strings, do I need to buy more?

Not right away. But you will need to replace strings fairly often. Generally, when you purchase a new guitar, the guitar will have been strung up with a fresh set of strings. Depending on the type of strings that are already on the guitar, they'll last for a little while.

The life of a string depends on a few different factors: type of string (coated or uncoated - I'll address this later), how often you play, how aggressive you play, the environment in which you play, and how much you sweat when you play. These are all factors that can impact string life. Because this varies so much depending on the individual player, it becomes important to be able to identify when strings need to be changed.

How do I know when to change my strings?

There are a few telltale signs that will let you know when the strings have reached the end of their lifespan. Of course, if you break a string, you'll need to replace it, but if you're not a very aggressive player, that may never happen. So here are some things to look and listen for:

• The coloration of the strings has begun to change - Strings will frequently be a bright copper, bronze or steel color when they're new. After a while, you'll notice that color has dulled or gotten rusty. You may not see the color change across the whole string, but it will be more prominent in areas of the string where your fingers or pick have been touching them.
• They don't sound as good as they used to - When you first start playing on a new set of strings, you'll hear a nice bright tone (different types of strings will have different tones, but you'll begin to recognize the sound of your new strings). After a while, the strings will start to lose that tone, and begin to sound dead. The progression to that state is gradual, but if the guitar isn't sounding as good as you remember, it's probably time for a string change.

 What kind of strings should I put on my guitar?

There are several factors that come into play with this question - some more general and some specific. We'll start with the general:

1. Get the right strings for your guitar type  - In broadest terms, there are different strings for different types of instruments. Electric strings for electric guitars, acoustic steel strings for acoustic steel string guitars, classical strings for classical guitars, etc. It seems like an obvious distinction, but when you're a beginner and you're looking at a giant rack of strings (or list of strings if you're looking on a site like Amazon or Musician's Friend), the differences can be subtle enough to be overlooked. For instance, if you look at the two boxes of strings below, it may not jump right out at you that one is for acoustic guitars and one is for electrics. But in the lower left, you'll see that one is for acoustic and one is for electric. Again, it may be obvious, but maybe not.
*A side note on the distinction between acoustic steel string guitars and classical guitars: While they are both technically acoustic guitars, it's very important to use the right string for your instrument. They are not only strung up in an entirely different way, but classical guitars use nylon strings, whereas acoustic steel string guitars use metal strings. Attempting to put steel strings on a classical guitar could potentially cause significant damage to the guitar.

2. Coated vs. Uncoated - Elixir, the brand pictured above, introduced the coated guitar string several years ago and, since then, there are a number of string brands that have jumped on to the coated string bandwagon. The biggest advantage of coated strings is that coated strings will last up to five times longer than an uncoated string. Coated strings do have their detractors, however. Some feel that they have to sacrifice sound quality when using a coated string. This was the case years ago when coated strings were first introduced but, in my opinion, there is very little, if any, reduction in sound quality when using coated strings. 
3. Choosing the specific type of acoustic string - There are a few different string types for a steel string guitar, but the main types that you'll likely be choosing between are 80/20 Bronze and Phosphor Bronze. 80/20 tends to have a brighter sound and Phosphor Bronze is a more mellow sounding string. D'Addario's website has a cool slider that allows you to see the qualities of each string type. Check it out here. 
4. Gauge - The gauge refers to the thickness of the string. You'll see a range of gauges from extra light to heavy. For beginning guitar players, you'll want to start with extra light or light-gauge strings. The heavier the gauge, the harder it is to fret. But you may find the sound a little soft with extra light strings, so I tend to prefer Lights. Different guitars are better suited for different string gauges, so you may eventually want to graduate to a medium-gauge string if you have a dreadnought, but for anyone starting out, go with light-gauge first.
5. Brand - There is no right answer to this question. Ask 10 different acoustic guitar players which brand they prefer and you'll likely get several different answers. I even have different preferences depending on the guitar I'm playing. 

Recommendations

Admittedly, this is a lot of information, and probably more than you wanted. So, if you're just looking for some recommendations, these are some of my favorites:

D'Addario EXP16 Coated Phosphor Bronze Acoustic Guitar Strings, Light, 12-53

Elixir® Strings Acoustic Phosphor Bronze Guitar Strings with NANOWEB® Coating

Martin SP 7100 Phosphor Bronze Lifespan Coated Acoustic Strings Light