Purchase a good beginning bluegrass guitar instruction method. These methods typically span several books, starting with the basics of reading music (standard or tablature), and moving through more advanced techniques. Keep instructional material handy as you develop your skills. Learning the principles of bluegrass playing is easy, but perfecting your skills is an ongoing process.
Learn tablature. A lot of bluegrass guitar music is written in tablature, just like other types of guitar music. Tablature is a simplified form of reading music that uses lines to represent strings and frets and numbers to represent the notes to be played. A good beginning method will include tablature reading instruction that can help you read bluegrass music written in this format.
Choose a simple bluegrass classic song like "Wildwood Flower." You can purchase this music from a music store, or it may be included in your method book.
Use this song to practice cross picking techniques, which is one of the foundation techniques used in bluegrass guitar playing and the technique that most distinguishes this type of music. Cross-picking is using a pick and your fingers to create a syncopated rhythm across three or more strings on a guitar. It takes time to develop this skill, but mastering the cross-picking technique is the key to playing bluegrass guitar.
Learn as many chords used in bluegrass music as you can. A beginning method will introduce chords you'll need gradually. Commit these chords to memory with regular practice and combine them with your cross-picking techniques to widen the scope of your playing repertoire.