RHYTHM
In the early days of bands, the gutar as thought of as part of the rhythm section, along with the drum kit and bass. To this day, you'l see bands with 2 guitars. One plays lead guitar playing riffs and solos. The other is the rhythm guitar, often playing chord progressions which offer support to the song's pulse, or rhythm.
Rhythm guitarists play chord progressions throughout the song. Within a song's measure different strumming patterns can be used. These different patterns add some interest to your playing, but their role is still to provide rhythm.
Strum patterns are great and essential for beginners. However, more advanced players will play more by feel than using an actually pattern. Even with this, they still provide a rhythmic pulse to the song and are great for beginning and even advanced players.
Place your fret hand against the strings Lay the side of your hand against the strings Varying the pressure will produce different sounds
Rhythm guitarists play chord progressions throughout the song. Within a song's measure different strumming patterns can be used. These different patterns add some interest to your playing, but their role is still to provide rhythm.
Strum patterns are great and essential for beginners. However, more advanced players will play more by feel than using an actually pattern. Even with this, they still provide a rhythmic pulse to the song and are great for beginning and even advanced players.
Whether hitting the strings or not, keep the hand moving down and up.
Tips
Never Stop Moving Your Strum Hand Down and Up
While you're strumming the hand should never stop moving down and up in time with the music. Strum down on beat and up off beat, whether hitting the strings or not.
Strum With A Relaxed Wrist
Strumming should come mostly from the wrist. There will be some movement of the forearm, but mostly the wrist. The tip should be slightly angled to produce a softer, more pleasing sound and allow it to move through the strings easier.
Use A Thin Pick And A Loose Grip
The idea with strumming is to create a flowing sound. A thin pick will be less likely to get caught in the strings. Keeping a loose grip on the pick will also help with this.
You Don't Hit All The Strings With Each Strum
Hit all the strings on the down strum, or most of them, but on the upstrum you only need to hit the highest 3 or 4 strings. Of course, a lot of this comes down to the song, but as a general rule hit all strings on the downstrum and the highest strings on the upstrum.
Vary Where You Strum
Strumming near the bridge will produce a brighter sound while the further you move away from the bridge will create a darker sound.
Strum Patterns
There are a lot of strum patterns out there. When you become advanced you'll usually make up your own as you understand the song and feel the beat. That said, it's always good to start off with predefined strum patterns.
Straight
These patterns always have a down strum on each beat. These are the most simple patterns, but they can sound good if done correctly.
Bass Note
These patterns are used a lot in country music, especially the older country music. These patterns usually start off by picking a single bass note before strumming. The bass notes are usually done on the 1st and 3rd beats.
Syncopation
Syncopated patterns remove one or more of the on beat strums. By skipping a strum on beat, you startled the listener and it causes them to actually listen. The most popular strum pattern is actually syncopated, the universal strum pattern missing the 3rd beat strum.
Accented
Changing the dynamics in your strumming also adds interest to your playing. With accents, you raise the volume of a particular strum, making the listener's ears perk up.
Muted
Strumming muted strings creates a sound reminicent of a bass or snare drum. There are various ways to mute strings.
Technique