Have Discipline - The most important thing you have to do in order to advance in your skill with the classical guitar is to practice regularly. This of course you already understand but in order to do this you might want to make yourself a schedule and stick to it. Decide in advance what days of the week you can practice, pick a time and stick to it. Block out at least one hour for each session. If you can do this at least five days a week your ability with the guitar will advance very rapidly.
Listen to the music - The biggest problem for a beginner is the physical challenge of learning how to use your hands and fingers; so almost all of your focus is on this. The intermediate guitarist learns the finger position then focuses on how to play the music with feeling. You should make this a priority early in your playing. One of the best ways to do this is to run a tape recorder while you are playing then listen to it afterwards. This way you can concentrate on how the music sounds without having to focus on your hands.
Establish a repertoire - You should establish a set of pieces that you will memorize. This can be as few as five pieces or as many as ten. But you should decide that you will memorize these pieces and then you should practice them, with memorization in mind, at every sitting.
Use Different Learning Techniques - Everybody learns differently and we all have strong ways and weak ways of learning. You should try different learning techniques and see which ones work best for you. You also get the benefit of bringing a well-rounded approach to your learning.
Here are some different techniques you should try:
Reading sheet music - This is a great, but slow, way to learn the language of music and will over time dramatically enhance your ability to play.
Work with an instructor - Some people establish a rapport with an instructor and do very well when they have someone they can ask questions.
Practice with friends - camaraderie is a great motivator. It will keep you playing.
Purchase a book with a cd or dvd - Having the sheet music along with a video or cd that plays the music will engage more of your mental faculties at the same time.
Download instructional videos - You may be a very visually oriented person and how a classical guitarist places his fingers may be an excellent way for you to learn
Try learning pieces directly from music you hear on CD's - this is an excellent but difficult technique. If you put some time into this your ear for the guitar will improve dramatically.
There are many ways you can quickly develop your skill as a classical guitarist. The two most important things to remember are that you should have the discipline to practice regularly and that you should try different techniques because some techniques will work better for you than others.