Fingering: In most instances, the first finger covers the 1^st and 2^nd frets, the second finger covers the 3^rd and 4^th frets, the third finger covers the 5^th and 6^th frets and the fourth finger covers the 7^th fret (and sometimes the 8^th).  For particularly complex passages, you may need to bend these rules.

Pick Direction:  In the vast majority of playing, pick direction is standardized, with notes on the beat (1 2 3 4) played with a down stroke and notes on the off beat (the ‘and’ in standard counting) played with an up stroke.  Playing with the correct pick direction is very important and you should work on making it second nature.  If you don’t use proper pick direction, you can find yourself tripping over the strings.  In addition, pick direction affects the tone with which you play.  The down stroke produces a stronger note than the up stroke, as it is easier to vibrate both strings with the down stroke.  Because of this, the down stroke is used on the beat, since most music requires an accent on the beat.

In 4/4 time, a series of 4 consecutive quarter notes will all be played with a down stroke, whereas a series of 4 consecutive eighth notes will be played down-up-down-up. 

If a song has a lead in starting on the off beat, start with an up stroke. 

There are some exceptions to the rules above.  Most notably, Irish jigs are played in 6/8 time and the picking pattern used is down-up-down down-up-down.  This is done to get the proper accents for jigs.

Some Bluegrass and Blues tunes use all down stokes to produce a more powerful feel.

Keep it loose:  Motion in both hands should be fluid and easy.  Don’t tense your muscles.  If your hand or arm muscles become sore or cramp, this is probably a sign of too much pressure – such as holding the pick too hard or pressing down on the strings too hard.

Experiment:  This applies to all aspects of playing.  There are many things that affect the tone you produce.  Experiment with different strings and picks.  Experiment with different pick angles and moving the pick closer to and further from the bridge.