This is something I waited way too long to try. I never really had a big problem with frets buzzing, but having all of your frets perfectly level and polished is a wonderful thing.
There are numerous ways to approach this task, and please bear in mind that this way works perfectly with an instrument with a flat fretboard, whereas the technique would be a little different with a radiused neck.
I ordered myself a fret crowning file from eBay. This one was around £25, and came complete with several grades of sandpaper from 800 to 2500 grit, a spring steel fretboard protector (to use while sanding) and a gummy rubber to clean the file. The file itself is concave and fits neatly over an individual fret, it is a diamond file and will give a good and smooth result quickly. They are custom made by a guy in the UK. Link here
To begin with, clamp the guitar down to you bench/table. I used some soft materials to prevent any scratches to the finish. I also masked off the pickups, so I didn't get any metallic dust in there.
Use a felt tip pen to draw a line straight across the tops of all of the frets. I used one of my daughter's Crayolas as they are easy to wipe off in case I slipped. This will be your reference point, as it will highlight any lower frets as you level them.
Levelling - this is the step that would differ if your fretboard had a radius (of course you can buy fret levelling files for this purpose, and I have heard of sticking sandpaper in your radius sanding block and using that). I ran the finer surface of my sharpening stone back and forth across the fretboard a few times, being careful to apply equal pressure. I carried on until all of the pen marks had gone.
Notice the flat tops on the frets. The two on the left side of the photo have had the pen line redrawn on them. Now it is time to recrown them.
With the crowning file, a few passes across the top of the fret will bring back the original rounded top. You want to keep going until your pen mark is just a very thin line across the middle of the fret. One you're happy with it, time to polish them up.
There are two ways to go about polishing the frets after crowning: Do them individually, using the spring steel fretboard protector and progressing through the grits (800, 1000, 1200, 1500, 2000, 2500) on each fret. This took ages! The second time I did this job I simply masked off the entire fretboard (leaving the frets exposed of course) and sanded the whole lot at the same time lengthways. This was much quicker, and I was happier with the result.
Once you're happy with the level of polish on the frets, all that's left to do is to gently brush away any metal filings and dust from the fretboard, and get the strings on.
And there we have it. Despite having no real issues before, the overall feel of the guitar is greatly improved. Of course, if you are experiencing buzz from uneven frets, this fairly simple process will make a huge difference.
-RK
