Here are some my tips for staying on track musically and some motives that I live by. These seem to help me; perhaps they can help you.
1. Stay a Fan First - No matter what stage you are at, you must always remember why you started. If you lose your pure passion for listening to music and keeping up on your favorite players/bands; than honestly where can motivation come from? Scott Henderson is famous for saying "without input, there is no output." Always stay a fan and no matter frustrated you become, you will never lose sight of how much you simply "love to play."
2. Have Patience - We have discussed this before. It takes time; plain and simple. You do have the odd virtuoso that comes out of the womb playing Mozart and GNR; but most of us work hard, and have patience. Don't overdo it as some things simply take time to register in your brain and within your muscle movement. You will get there, believe me.
3. Confidence is Key - Without confidence in your playing, people will see right through you and hear that lack of confidence. You hear all these bands with very simple guitar playing and some guys that can barely play rocking stadiums. It is the confidence and passion in what they do that drives them, and ultimately results in some shade of success. Be confident in what you do, and people will listen.
4. After School Special - Going to music school was my main motivation for moving to LA. It also changed my life and prepared me to have a career in music. However; it was in music school that I felt the most frustrated. You are progressing every day, and you simply won't see the results until after you are done and out there PLAYING WITH OTHERS, MAKING MUSIC. I still take lessons. I asked my teacher after music school, how long did it take before you felt you had shed your "music schoolness" and stopped over analyzing your playing. His answer; "about 10 years." Just know you are not alone in your struggles.
5. It Never Ends - Like Lawrence said; you can practice all day and still find something you need to work on. That is the beauty of it. If you could sit down with any of your favorite guitar players, I can bet you anything all of them will tell you they still aren't where they want to be, and need some serious practice. I am also certain some of them could learn a thing or two from you.
6. Be You - My last point; it is important to find an identity. You will find throughout your musical life time that you will be inspired to take on many things. However, through time those things were surface by which define you. Find those things and make the most of them. To have a musical identity strengthens your confidence, and allows to grow into the player you want to become.
Take these as words of motivation. We all have been there, and many ways still are. Stay focused and know you WILL be where you want to be.
Douglas Showalter