The most important factor in improving your guitar playing is to practice regularly.

The difference between regular practice and regular playing

All practice involves playing the guitar, but not all guitar playing counts as practice! If you just pick up the guitar and noodle through some licks and play through some very familiar riffs, then you probably won't progress very fast, even if you do it every day. Even worse if you watch TV at the same time, chat along to your brother or your housemate and stop to answer the phone.

The difference between practicing regularly and just playing regularly is focus. The first step to focus is to eliminate distractions. If you have films or TV on when you are playing, then you're not practicing. And if you are expecting to be interrupted as you play, then you aren't focussing, and that's not practice either. Of course, freeing yourself from distraction is important, but to focus you also need something to focus on. What does this mean? Well, you need to find an element in your playing to improve upon. There's no need to overthink this. Say, for example, you want to improve your alternate picking - try some alternate picking exercises and play through them to gain speed and accuracy. Or if you are having trouble with certain chords, then use your practice time to play through some songs that use them. As simple as all this sounds, it's important not to overlook it - if you haven't picked an element of your playing to improve upon then you are not practicing.

So how do you move from playing regularly to practicing regularly? When you play guitar, clear away some distractions, including television, telephones, instant messaging and anything else that might interrupt you or draw your attention away. And then play through 1 or 2 things that will improve on your playing and give them 100% of your attention.

Finding time to practice regularly

I was 13 when I started playing guitar. I had school, but didn't have to work. My little sister tended to hog the television and watch lame shows I wasn't interested in, and our parents didn't make us do too many chores. Most of my friends lived on the other side of town and at that age there wasn't that much to do or go to anyway, apart from play computer games or occasionally go and see a movie. So it was actually kind of easy to find the time to practice! I used to play obsessively every evening and often all afternoon on the weekends. Fast forward to adulthood, and now we all have jobs, bills to pay, and all the usual domestic chores of meals, laundry and so on that eat away at your day. There are also all the extra freedoms and options to spend leisure time how we'd like! These things all make it a lot harder to practice regularly.

The one thing that really helps is to schedule practice times, and to stick to them as much as I would to something like an important doctor's appointment.  I actually write it down.. something like this:

6:30-6:35 stretches and warmups
6:35-6:45 sweep picking arpeggios
6:45-6:55 coordinating singing and playing together
6:55-7:00 play through a song

That's just an example, but you get the idea.  I then stick to this religiously!  My housemate knows not to talk to interrupt me at my scheduled practice, and I turn my phone off.  I know some of you will panic at the idea of not being contactable 24/7, but it's okay!  You'll live.  The important thing is to stick to it - and part of sticking to a scheduled practice time is to be realistic.  You might feel good by writing out a plan that takes 3 hours a day, but if you don't do it then it's not helping!  In fact, even worse, by writing out a plan that you can't follow through with, then you are putting yourself into a habit of ignoring the schedule you set for yourself.  We humans are creatures of habit, and if you start setting practice times and then not doing it you will find it so much harder to actually get anything done.  I like to schedule something every evening Monday-Thursday, and then leave myself Friday nights and the weekend purely for social life, band practice and such things.  This is just what works for me, you'll have a different weekly routine so see what you can do.  Good luck and have fun!