I say you can practice effectively if you commit to only 15 minutes each day. Will you become a virtuoso? No. Can you get better? Yes. If you don't know how to practice try this.
- Commit yourself to 15 minutes of focused practice 5 days a week. 7 would be better but 5 will do for now.
- Set very specific goals for your practices
- What do you hope to get better at? A certain song. A specific technique. Both. Maybe your left hand needs work. Maybe the right hand. Whatever it is, choose one thing and go after it to the exclusion of most other things. Remember this is for the 15 min. practice session. If you can find more time you can go over more things.
- Spend 3-4 minutes warming up with scales, arpeggios, and other fingering exercises. If you don't know your basic scales or arpeggios maybe you should spend the whole practice on scales for a few weeks and get those to a point where you don't have to think about the fingering patterns to much. The goal here is to slowly warm up with good muscle memory in the fingers. If you're a rhythm guitarist you could spend a few minutes practicing basic strumming patterns with a metronome.
- Again this could be anything. A song. A technique. Learning to tune your instrument. Chords. Scales. Speed. Tone. Dynamics. Whatever your goal is go after it. Most importantly go SLOW!
- The 15 minute practice session is all about QUALITY. Forget about playing things fast. Or doing anything quickly. You want to make sure that you are doing things right. Play through your piece slowly making sure everything is working smoothly.
- Don't move on to another goal until you've improved. This could take a while but after a couple of weeks of playing the same song or scale you'll be amazed at how much better you've become at that.
- Now you can move on to another goal. A new song. Playing that song faster. Whatever. Maybe you can use your newly improved song as a warm up if you play it slowly enough.
- If you're not seeing improvement after a couple of weeks:
- There could be a few reasons. Most likely you're trying to play it to fast. You also might not know where your fingers go. This is very important. I've already written about this here: http://chummersmusic.blogspot.com/2009/09/strategies-for-practicing-effectively.html Maybe you just need to spend more time with the problem. Try it for few more weeks. See how it is after that.
Hope it helps.