First, take a look at the strings. It might be time to replace them with new ones.

Have they accumulated a film? (You might want to look on the underside and see if the dirt has built up there.) There are a number of products designed to extend the life of strings, but if you really want to go the economy route, then simply wipe them down with a slightly damp cloth. This is better than nothing.

Can you see dirt and grime building up on the fret board? (This is minor, but if you're cleaning the grime, you might just as well clean this surface during the string change.) You might want to clean this with a slightly damp cloth or a good guitar cleaner. There are people who recommend using the finest grade of steel wool and abrade extra tough dirt off of your fret board. I haven't had the need to go this far yet, and would use extreme caution and go easy on the elbow grease to be sure not to scratch the finish on the wood.

A long term sweat and dirt buildup can eventually damage the glue joints and possibly warp your instrument (this could happen after a long period of exposure without any maintenance). I'm would not be considered an avid "guitar polishing guy" but and occasional cleaning of the fret board will extend your guitar's life.

If this doesn't help or fix the problem, the solution might require the expertise of an experienced guitar technician. There are some things you probably should do to pinpoint the exact location of the buzz, however, I would never recommend that you grab tools and try to adjust a guitar on their own. Learn from a person with experience and your guitar won't become a field casualty.

Check and see if the buzz is consistent along the length of the neck (check from the open strings to the small spaced frets toward the bottom or near the body of the instrument).

Pick each one of the strings open without fretting any notes.

Begin fretting each string at the first fret then move down toward the body. You might not need to successively fret each and every position, of course if you're compulsive about your instrument, then go ahead and check each fret.

Make yourself a note as to just where the buzz appears and where is goes away or stops. If the buzz continues and remains from the open strings and doesn't go away even during fretting of the highest pitched frets, the problem is most likely in the bridge or the saddle assembly. Are there any parts that are loose? You might want to have a guitar technician work on this area.

Ask if they'll let you view the repair process. I have gleaned a lot of maintenance knowledge and ideas by being present during a repair and asking simple question while someone was working on my instruments. (Try not to get in the way, guitar technicians will tolerate your presence and questions, if they don't get annoyed by your presence.)

If you pin down the buzzing to the section of your guitar neck closer to the main body:

You might need to have the strings saddles adjusted upward so they'll be higher and farther away from the first frets they go over. If you decide to do this yourself, then make the adjustments in small increments so you don't raise the action more than necessary. If the height of the saddle won't adjust up enough, then a truss rod adjustment is probably needed (see description below).

There might be a fret or two that needs to be sanded slightly to eliminate an inconsistent span of the frets on the neck. Don't try to make this adjustment yourself. If you happen to go too far, the damaged and mutilated fret will become permanently out of pitch.

If the fret buzzing is closer to the middle of the neck (towards the head or nut):

Inserting a thin shim under the nut might raise the strings high enough to eliminate the strings' buzzy contact with the frets. This can be a bit difficult if the nut is glued, but for those of you who put up with the locking variety, you can easily remove the nut and insert a small, thin piece of paper or some foil under the nut. Remember though to take it in increments; it can be very hard to play those neoclassical licks with an action that is to high.

The neck of your guitar may need to have the truss rod adjusted. A truss rod is a rod of metal running the length of a guitar's neck. Using a tool to turn it to the left or right, you cause the wood of the neck to bow in or out. Out of all the adjustments mentioned so far, this is the most dangerous to your guitar's neck and should with out a doubt be handled by a guitar repair technician. Should you turn the rod too far (even be it a fraction of a turn), you can splinter the guitar neck. This step is a good one to watch and learn. A minute adjustment can make a huge difference in the bow of the your guitar's neck.

Each and every adjustment might necessitate other adjustments to preserve a proper action. Try cleaning the neck and getting a new set of strings, this might solve your problems. If you are a strummer and are using light strings, you might want to raise the action and/or move to a bit heavier gauge of strings. Don't hesitate to take your instrument to a good guitar technician of your choice. You might well learn quite a bit for future care and maintenance of your guitar.

I hope reading this helps. Enjoy your music!!