Your rhythm and beat will be determined largely by what particular style of rock you want to make. Punk rock has a faster, driving rhythm, heavy metal uses a 4/4 time signature (the beat is a quarter note lasting 1 second and there are 4 beats per measure), reggae rock is syncopated (beats are played off the rhythm). Search online to find out what rhythm and beats the particular genre of rock music you want to play uses. Many of the most famous rock songs use power chords rather than traditional ones to give the music a less smooth, edgier sound. Power chords are formed by fingering the main note of the chord with your first finger on the top string of your guitar, then using your third and fourth fingers to press down on the 2 strings below the top string 2 frets down the neck of the guitar.  The G power chord, for example, would be formed by pressing on the third fret on the top string, then the fifth fret on the 2 strings below the top string.  Nirvana’s song “Smells Like Teen Spirit,” for example, uses the power chords for E, A, G, and C.  Power chords are particularly popular in grunge music. Acid rock songs use the same type of chords, but they distort the chords by using a distortion pedal hooked up to the amplifier. Indie rock, on the other hand, tends to go for a smoother, softer sound, and may even use traditional chords. Glam rock also uses smoother sounds, and tends to experiment with music from other genres entirely. Electric guitars have been the foundation of rock songs since the beginning. While you’re writing your song, use an electric guitar as the accompaniment and to help develop your melody. Once your finished writing your song, you can add in instruments like the drums, bass guitar, and keyboard.  You should also remember to strum your guitar like you’re trying to break the strings. Rock music isn’t rock music without a destructive vibe. Funk rock, for example, emphasizes a heavy beat from the bass guitar and drums. Singer-songwriters like Joan Armatrading tend to focus heavily on melody instruments like guitar and piano and use other instruments mostly just to achieve a fuller sound. Every great rock song has a killer instrumental solo, almost always one with an electric guitar. To write your solo, play around with scales in your song’s key and try adding in bits and pieces of your melody. Try different combinations to see what you come up with and do what you can to really show off your skill.  Psychedelic rock in particular features long, improvised instrumental solos, usually by a electric guitar. Punk rock, on the other hand, tends to see instrumental solos and pretentious and unnecessary. The iconic guitar part in the Guns N’ Roses song “Sweet Child O’ Mine,” for example, is a simple variation of a scale that Axl Rose heard guitarist Slash playing in rehearsal.

Summary:
Decide on your rhythm and beat. Use power chords. Start with an electric guitar and then add in other classic rock instruments. Feature an instrumental solo.