If you’d like to learn how to sight read, I highly recommend these two books: Melodic Rhythms for Guitar, and Reading Studies for Guitar.
Both are written by master jazz guitarist and arranger Bill Leavitt, and the reason I prefer these two books is because of how easy the notation is to read and the progression of bringing you from a complete novice to a sight reading jedi. When I was at Berklee College of Music I took lessons from the best guitarists in the world, like Dave Tronzo, Dave Fiuczynski, Tomo Fujita, Joe Stump, Mike Idhe, and many more. What was the one thing we never practiced in the classroom together? Sight reading. The reason is because you can’t have somebody physically show you how to sight read. It’s a very intimate exercise you have to do on your own with a guitar, a piece of sheet music and a metronome.
Sheet music for practice is very easy to come by in the age of the Internet, but I definitely recommend signing up for Guitar Super System to access a large library of sheet music that has been hand picked to provide a wide array of different positions and musical situations.
An important thing to remember about sight reading is to never read the same piece of music more than a few times over, because you will begin to memorize the music and train your muscle memory, rather than your sight reading skills.
One of my teachers, Dave Tronzo, would take a sheet of music and read it normally, left to right, then read it backwards, right to left. Then, he would flip the music over, read it left to right, and then read the upside down music backwards, right to left. That’s an extreme example of how good you can become at sight reading, but just know that if you practice sight reading with new music every day for even just ten minutes, you will see a vast improvement in your sight reading skills in just a few weeks.
Prepare to play the most meaningful music you ever have.