Music isn't just a bunch of notes and chords played together at a constant volume level. Music is dynamic. The notes, chords and overall harmonic and rhythmic content can be simple or complex and any or all of those elements change from very soft to very loud in the blink of an eye. You can control the dynamics of your playing by learning a variety of picking, strumming, and fretboard techniques.
There's nothing complicated about the basic technique for picking and strumming the strings on your guitar. You simply strike the strings with a finger or a pick and sound is produced. On the other hand, there are some fancy tricks for creating a variety of subtle changes to your sound and adding effects to the notes and chords you play.
I want to reiterate something I have mentioned elsewhere because I believe it is important. When you practice chords and/or strumming and picking, don't stop your strumming hand if you are having trouble forming chords or playing lead fills. Keep your strumming hand going steadily and your fretboard fingers will eventually catch up. In fact, it is probably better to practice chord formation first without strumming. Let them sink into your mind, and then start strumming. I think you will find that "muscle memory" will take care of the chord formations once you know how each one is formed. Stopping each time you make a mistake on the fretboard only causes more frustration. Always relax and take your time. Use a slower tempo when you start practicing something new. Speed things up slowly until it becomes second nature, which it will!
Guitar picks (plectrums) come in a variety of stiffness. Some are flexible and some are very rigid. There are also multi-purpose picks, which are not overly flexible or rigid. You should choose a pick that feels comfortable and allows you to control your picking and strumming with ease. The general rule of thumb is this: soft (flexible) pick for strumming rhythm and medium--hard to hard for picking leads or fills. Keep plenty on hand, because they often get misplaced.
There is a technique you can use with a medium-soft pick that allows you to also have the benefits of a hard pick when you're playing a lead or fill. You simply shorten the pick between your index finger and thumb slightly, which makes the pick more rigid. When you want to return to strumming, just lengthen your grip on the pick.
If you want a consistently clean sound and clean notes, you should pick and strum the strings lightly. Acoustic guitars have a limited dynamic range - they can be played only so hard without losing their tonal quality and only so soft and still be heard. Of course, you could add a pickup to an acoustic guitar to increase the volume but it would still have different sound qualities compared to a solid-body electric guitar. Electric guitars differ from acoustic guitars in several ways. They are not as limited in dynamic range because the power output of the amplifier determines how loud or soft and electric guitar can be. Electric guitars also have volume and tone controls, which along with your amplifier's controls allow you to change the tone and volume of the guitar drastically, regardless of your picking and strumming technique. However, in both types of guitars, relatively soft strumming and picking are best if you want clean clear notes.
Some genres of music like Heavy Metal, Punk, and Hard Rock, obviously don't subscribe to the "easy does it" philosophy. There's nothing wrong with that. They are based on the "full steam ahead" approach. Of course, these types of music focus on loud, overdriven electric guitars and amplifiers, but, the picking and strumming can be soft or hard and you would hardly know the difference. Still, there are some subtle picking techniques used in these genres which add to the "in-your-face" attitude.
One picking technique often used is the "pick edge attack". Instead of using the flat face of the pick, you turn it slightly and play with the edge of the pick at an acute angle to the strings. This adds a "punchiness" or "bite" to the notes and a harmonic ringing as well. This technique takes some practice before it can be mastered. You can add some variations to it by using some of the fretboard fingering techniques described below. I should warn you that being over-zealous with the "pick edge attack" could cause a lot of broken strings and frustration.
In the sample below you will hear a string being picked normally followed by the string being picked using the Pinch Harmonic technique.
This technique provides a wider range of notes and tones (harmonics in higher octaves) than can ordinarily be played on a guitar. Pinch Harmonics are notes produced by using a slightly different picking technique. Hold your pick with just the tip protruding between your thumb and forefinger(s) as in Figure 17-1. Pluck a string with the pick and also lightly brush it with the edge of your thumb (between the fingernail and the knuckle). The root note (called the Fundamental tone) will be mostly cancelled but a much higher note (a harmonic) will be heard. The actual pitch of the harmonic depends on where the pick and thumb strike the string. As you move the picking hand toward the bridge of the guitar the harmonics will be higher pitched. Conversely, if you move toward the neck the harmonics will be lower in pitch. You will need to experiment and practice the technique to find the harmonic nodes that provide the pitch or sound you want. Vibrato and Bending can add a variety of effects to this technique. It is also much easier to play and hear this technique if you turn the gain up high (more distortion) on your amplifier. However, it is possible to play pinch harmonics using a clean electric sound or even on a an acoustic guitar; It just takes more practice because it requires more accurate timing and touch. As always, new strings always help any technique sound etter.
Muting causes notes to sound "muffled" because you are intentionally stopping them from ringing. Generally, you pick or strum continuously as you mute the strings, but there are some exceptions (Read STRING KILL below). You can mute the sound by using the ball of your hand across the strings at the bridge. There are actually two techniques used. One involves how far your palm (or the ball of your hand) extends beyond the bridge toward the fretboard (although the range of the distance is generally within a centimeter of the bridge). The other technique depends on how heavily you press the ball of your hand upon the strings there. With practice, you can vary the placing and pressure of your hand to adjust the amount of muting.
There are three basic ways to strum: Up and down strokes, all up strokes, and all down strokes. Of course, you can vary the ratio of up to down strokes in all sorts of complicated ways and you can use some very eclectic rhythms. You could even play some strings on down strokes and other strings on the up strokes. Each of these techniques provides a slightly different musical effect and the only limitations to using them are how fast, and (more importantly), how accurately you can strum. Finding the "range" of your strings (that is, "feeling" the distance between your top and bottom strings and those in between them) comes with practice. Generally speaking, when you strum your hand is not resting on the body of the guitar and you wrist does most of the work, not your arm.
Down strokes have a slightly different sound from upstrokes, and, regardless of whether you are playing an acoustic or electric guitar, when you strum the strings close to the bridge you get a brighter sound (more treble). If you strum them where the fretboard meets the body you get a more mellow sound. You can mix these sounds together by using the Figure Eight strum technique.
Imagine a large 8 laying on its' side and fitting between your bridge and just beyond where the fretboard meets the body of your guitar. Let's start with a simple pattern. The object is to play 1 down stroke at the bridge, 1 upstroke between the bridge and the fretboard, down stroke at the fretboard (where it meets the body) and another upstroke between the bridge and the fretboard. Like this:
1) Start with a down stroke at the top edge of the fretboard (where it meets the body) and then move your hand down around the top of the 8 (clockwise) and then up and back toward the bridge.
2) Play an upstroke halfway between the bridge and the fretboard as you move up and back toward the bridge
3) Play another down stroke when you reach the top edge of the bridge and trace the bottom of the 8 (counterclockwise) moving your hand downward.
4) Move your hand back toward the fretboard and play an upstroke as you cross the center again as you move up and toward the fretboard.
Figure 17-2 shows the direction and the strumming points.
There are dozens of stroke combinations you could use with the "Figure 8" strumming technique. Two examples would be to first exchange the up strokes for down strokes, or, change the direction of the starting stroke (but start below the strings rather than above them).
The "Up Up" strumming pattern involves playing 2 quick up strokes after each down stroke, with a slight variation at the end of the pattern. It's like a drummer's paradiddle, except the "roll" is performed with one hand instead of two. You start with a down stroke and within 1/2 of a beat (eighth beat) you strum 2 up strokes. Let's take four beats and break the pattern down into its' components:
Beat One: Down, Up
Beat Two: Up, Down
Beat Three: Up, Up
Beat Four: Down, Up
Figure 17-3 shows when, and in what direction, the strumming should be for a single bar.
Try using the patterns mentioned above in a variety of ways and in different combinations while changing from one chord to another. Experiment with them and create your own patterns.