Memorize the notes on the fretboard. The fretboard is the long wooden part of the guitar where you form chords and play notes. It extends from the body of the guitar to the headstock, which is where the strings are tuned. Many new guitarists find that it is easiest to memorize the notes by putting gum-free stickers that have been labeled with the notes on the fretboard while they practice as well as purchasing or downloading a fretboard chart that shows the finger positions of all the notes on the necks.
Study the most basic guitar scales that are commonly used by guitarists. The major scale, minor scale, pentatonic scale, minor pentatonic scale and blue scale are the commonly used in rock music. While these scales are available online for free, most players find that having a book for learning and later reference is a good idea, particularly as you advance and want to learn more complex, specific scales.
Study the most basic guitar chords and a bit about chord theory. Start with the major and minor chords and move on to more advanced, less commonly used chords like sevenths, augmented and suspended chords. Learning a bit about chord theory will help you to understand the way songs are written, and this is especially important if you are interested in writing your own music later on.
Study and learn how to read guitar tablature so that you can play songs as you progress. In guitar tablature, each line represents a string, with your low E or thickest string show as the bottom line. THe numbers on the lines indicate where your fingers go on each fret. For example, a number 3 on the lowest string, would mean that you place your finger on the third fret of that string.
Purchase a book of guitar tablature that contains songs for which you have recordings. Practice along with the recordings as you learn the songs to make sure you aren't making mistakes.
Practice for at least one hour every day. Learning to play the guitar requires lots of practice, and if you don't practice the fundamental skills enough, you never will master them. And that will keep you from advancing as a player.