Practice, Practice, Practice
One question that seems to come up over and over again from beginning guitarists is "how long will it take me to play like ____". This question is obviously quite difficult to answer. There are many factors that come into play when learning a musical instrument. "Have you played or studied a musical instrument before? Do your parents play? How much time do you have to devote to learning the guitar?" There is, however, an answer that I give that is extremely broad in its implication; practice.

Consistency in your practice time is critical for developing the skills needed to play the guitar well. Along with consistency in practicing it is also important to practice smart; to have clear objectives/goals each time you pick up the instrument. Below are a few tips that will help you organize your practice time and get great results.

1)
Ritualize Your Practice Time:
Your practice time should be a holy moment. It should be something you do consistently, like brushing your teeth. An athlete would not be able to compete well if they only trained once or twice before a big competition. It is just not possible. The same goes for learning a musical instrument; you must be consistent. 30 minutes/day, 6 days a week will pay bigger dividends than practicing once a week for an hour. Make it a part of your day you could not live without.

2)
Rise Early:
This is never a popular practice tip, but very effective. Most people have a difficult time squeezing in enough practice time throughout their day. The solution: set your alarm clock 30 minutes to an hour earlier. Rising early will also give you a great boost of energy and make you feel successful throughout your day.

3)
Don't Neglect Your Technique:
Technique is the vehicle used for musical expression. If your technique is in bad shape how can you expect to play well? Spend a good portion of your practice time, for beginners I would suggest 50% of your practice time, honing your technique. You will not be disappointed.

4)
Have a Written Plan:
Put your practice goals down on paper so you can see what you need, or want, to accomplish in a week, month, year, lifetime. Having your goals in print forces you to evaluate where you currently are in relation to these goals. Sidebar: always evaluate how you are practicing and see if it is in alignment with your goals. If you goal is to make a living playing guitar? If so, are you practicing like it?

5)
Don't Confuse Practicing with Playing:
Picking up your guitar and playing a familiar piece or tune is not practicing, it is playing, or jamming. Practicing is designed to accomplish a specific goal: learn the first phrase of a certain piece, solo over the changes of a particular tune, balance and control of the "a" finger, etc. Note that we need to pick up the guitar and just play. Learning a musical instrument should be a fun endeavor, not just all work. When you practice, focus on your practice. When you play, let the fruits of your labor shine forth.

Practicing is a topic that deserves much more attention than can be provided here. Hopefully this will give you some ideas of how to get the most out of your practice time.