Fret buzz can be caused by a number of factors, including uneven fret height and a twisted or back-arched neck, but the most common cause of buzzes, especially with beginning players, is that they just don’t get the string pressed down hard enough behind the fret. That lets the string ride too high, which, in turn, allows it to vibrate against the fret instead of in front of it, as the string is supposed to do.
So, do you want to get rid of buzzes in your playing? Press down harder on the string with your left hand (for fight-handed players).
One more common flaw, closely related to the preceding one, can cause buzzes on acoustic guitar. That is when the player gets the string pressed down okay, but too far behind the desired fret. Again, this leaves room for vibration and slop on top of the fret. Just bring your finger as far toward the target fret as you can. That usually fixes it.
Now, just to make things a little more complicated, the laws of physics state that if you press down on the string too hard, you can “pull” the string out of tune, contributing to an out of tune chord. Out of tune chords sound weak and dull when compared to their in tune counterparts, so try to strike the right balance between pressing hard enough to avoid buzz, and not pressing so hard that your chords pop out of tune.
And remember, practice doesn’t make perfect. Only perfect practice makes perfect. Practice your acoustic guitar routines, exercises and songs slowly enough that you play them right; then you are ingraining habits of perfect playing that will gain speed as your skills come up. (The alternative is to burn your mistakes, arising out of trying to play hard passages too fast, into your brain’s “ROM,” and it’ll take twice as much work to break those bad habits before you can form good, new ones. Better to do it right in the first place.)
Go do something noteworthy!