Sight reading is clearly one of the least developed skills among classical guitarists. When performing in an ensemble situation, it is quiet shameful to make a bad impression on other musicians just because of our lack of sight reading skills. Also, learning new pieces often becomes a dreadful task since getting past the first reading stages can be a very tedious activity. There is no such a thing as a guitarist who was born a natural sight reader. Anyone who is good at it has surely put hours of practice into it.
When talking about sight reading, I believe that the guitar is at a disadvantage when compared to other instruments. Most instruments have fewer options of finding a given pitch. For example, middle C on the piano is accounted for by one single white key; the middle C key. Now, how many high E's can you play on the guitar? One in the open E string, one on the 2nd string 5th fret, one on the 3rd string 9th fret, and finally one on the 4th string 14th fret. That is without counting the 5th and 7th fret harmonics on the 6th and 5th strings respectively. But don't get discouraged, remember that other instruments also have their own challenges. For example, the violin is a non-tempered (unfretted) instrument for it intonation is a critical issue.
What would a violinist do in order to improve his/her intonation? Guess what? Practice! Practice a whole lot to overcome the difficulty. What do we guitarists usually do in order to become better sight readers? Sincerely, not much? maybe we lie down on the couch and watch TV! I hope you get my point. It is very easy to become a better sight reader. It is just a matter of getting off our butt to practice every day.
So, here you are, ready to tackle mountain of a task called sight-reading. The problem is that you don't know where to begin. Let's break down the problem and create a good strategy to aid our task:
1) Don't get too fancy. Start with single line melodies in the first position. Eventually move on, explore some "unknown" territory higher up the neck. It is a good exercise to figure out a melody in different positions of the fret board.
2) Set your metronome (you heard right, METRONOME) to a very slow tempo, and make it subdivide in either eighth-notes or sixteenth-notes.
3) Verbalize the name of each note simultaneously as you play it. If you like singing (or if you like to be annoying to the person next to you) add pitch to it. I personally don't worry about verbalizing sharps or flats, just call C sharp "C".
4) Give priority to the rhythmic flow rather than to note accuracy. If you can't figure out a note on time just move on to the next one. Imagine you are playing with an ensemble. They wouldn't stop and wait until you got each note right.
5) Read ahead, just like when you read a book or magazine article. Train yourself to keep your eyes ahead of what you are playing in order to anticipate what is coming next.
6) View notes as larger groups. If you see an ascending, stepwise, run of sixteenth-notes that start on C1 and end on C2, and there are no sharps or flats, most likely it will be a C major scale. Apply the same principle for arpeggios; look at repeated notes and quickly analyze what chord the arpeggio is outlining.
7) Don't worry about fingerings. Many times when sight reading we will run into very awkward and unorthodox fingering patterns. It is ok? don't let this slow you down. The task at hand is to read through the notes at the right time. Leave the analysis of fingerings for a later stage. You will notice that as you become a better sight reader you will start improving your fingering decisions on the fly.
8) Don't leave your fingers stuck to the fret board for longer than needed.
9) Simple rhythmic patterns are recommended. The learning of rhythm needs to be gradual. In the beginning stages of sight-reading will be useless, to attemp playing in a high position on the fret board, if the melody incorporates complex rhythmic patterns.
10) Add multiple voices gradually. Learning to read in bass clef is also useful, especially for those interested in arranging music or playing baroque continuo sections.
Practice, practice, practice and make sure to feel very guilty if you don't. Reward yourself if you practiced hard. Go for some ice cream or invite your girlfriend or boyfriend over for a movie ;-)