I´m going to go through the different techniques for using your pick, and of course I´ll start with the most fundamental one: Alternate Picking. It may seem to be an easy technique, at least when you read about it. All you have to do is to play up, down, up, down, up, down and you´re there. But it´s not that easy as it sounds, epecially if you want to become really good at alternate picking. As with many other techniques there are traps which are easy to fall in and there are times when your head will mess with your hands. But first, let´s look at the basics:
There are two symbols that you need to understand. The first one is the downstroke: ͆ . This means that you pick the string from above, downwards to the ground. And then there´s the opposite, the upstroke: ˅ . This means that you start under the string and pick it upward to the ceiling. These are the two motions that you should use in perfect symbiosis. And of course, as the name of the technique suggests, you should alternate between downstrokes and upstrokes.
Here´s a simple exercise to get you started, it will both give you a good understanding for alternate picking and some frethand action where you´ll use all your four fingers (which finger to use is marked out with numbers, eg. 1 is for the index finger, 4 is for the pinkie...):
This is not so hard, but probably a bit harder than it looks. Be sure to hit the strings at exactly the right time, so you´ll sync the left and the right hand. If you start out too fast, things will get sloppy and your alternate picking will sound bad.
Here´s another exercise, and just like the first one this is also a chromatic exercise. But instead of only using one string, here you´ll use every string. You start from the bottom, the heaviest string, and advance all the way to the top string. Once you are there, you move up one fret and continue the exercise, but now you´ll be playing the other way around - you start with your pinkie on the 5th fret of the top string and work your way down to the bottom string. And once you´re there, you´ll move up a fret again and continue to work your way up to the top string again in the same fashion as before. Then continue the exercise further up the neck in the same pattern as previously:
Many guitarists use the downstroke to emphasize the important notes, the 1 and 2 and 3 and 4 in a measure, which forces you to use an upstroke on all the syncopes. For example, if the phraze begins with a rest and the first tone you are about to play is a syncope, you´ll have to start with an usptroke. Like this:
Many jazz, latin and funk players has good knowledge of this, because the phrazing they use often a bit more sophisticated than what a rock guitarist would use. But this is valuable knowledge to rock and pop guitarists as well, because to emphasize the right notes in a phraze is often what makes the difference between a good and a great player. However, don´t build an absolute rule around this. Sometimes it will sound better to use a downstroke on a syncope, especially if you want this tone to stand out. I have also seen guitarists who strokes up and down in the air when they have a pause in a phraze, just to get the up and down motion going. This way, they will hit syncopes on upstrokes, for sure, but I think it´s a waste of motion. Sometimes, these guitarist will have a problem to really play in a free way, and the result is always a bit stiff. My advice is to become aware of when to use a downstroke or an upstroke, but don´t be a slave to it. Practice well, practice with awareness and practice every day, and eventually you´ll work the technique into your brain and hands. Then you will be able to use the technique well, without much thinking, and then you can focus on the music. And when you focus on the music, you don´t flap around with your pick when a phraze has a rest - there´s more important things to keep your mind on.
Practice alternate picking often, it´s an essential tool to becoming a great guitarist. And most important of all, practice in a good way, so you don´t get sloppy. Start at a low pace, and once your comfortable and don´t make any mistakes, move on to a higher tempo. There will be more alternate picking exercises on this page, for sure!