Keeping a consistently steady beat is one of the most important aspects of playing almost all music.  Many musicians have problems doing this including me.  Still, one of the best tools to help you overcome this is the metronome.  In order to take advantage of this tool it is helpful to have an understanding of rhythm and how the beat represents the pulse that underlies almost all music.  Although it's very helpful to know how to read music it's not necessary to use this technique as long as you understand where the beat is in relation to the rhythm you are playing.  Using this technique only requires a lot of patience married to the ability to count to two, three, or four.  The technique is simply stated as follows:

Play the section you are trying to learn with the metronome set to a tempo that is slow enough for you to play the part correctly without any rhythmic mistakes.  Once you feel comfortable at that speed move the tempo up no more than one notch at a time, playing the piece without mistakes.  Continue this process of increasing the tempo one notch at a time, playing without mistakes until you reach the speed at which the piece is to be played.

As I said before, this technique requires a great deal of patience but will provide the best results in the shortest amount of time. This becomes increasingly important when you attempt to play two independent patterns such as when playing a steady quarter note pattern in the left hand while having syncopated eight notes in the right or when strumming a rhythm on the guitar while trying to sing a melody to a different rhythmic pattern.  Slow it down until you can get it right.  If you have a hard time doing it slowly it's going to be that much harder to do right playing it fast.

[ed note: 20200420.  I will eventually expand on this to include comments how the metronome ensures you keep the beat steady, about what 'notch' means since the distance between numbers indicating the frequency of clicking on a metronome becomes less significant as the tempo increases and therefore can be greater,  how it is helpful to count aloud while practicing, the complexities involved when you try and do more than one thing, tapping your feet along with the metronome, what unit of time the metronome should beat at (quarter notes, eighth notes, sixteenth notes, etc), and my experience with this.  I will also make videos explaining this process as well as write articles on all the other topics (starting with the one's in maroon).  The reason I put this comment here is that this is the first article or tip that I am posting on this website!  I hope you have found it helpful.  Greg Shoemaker]