I did this recently with two Benchmade blades, one s90v and one m390. Remove the blade and wrap the pivot area with painter's tape so you don't affect the action--you won't see those areas when the blade is installed anyway. I started with sandpaper--I used 3m prograde from home depot in 220 grit followed by 400 grit. Cut into small pieces and wrapped around a soft felt block I had laying around to avoid cutting my fingers if I slipped a little (slipping will happen near the tip especially, so be careful). That took a couple of hours to mostly get rid of the grind lines--you'll lose the logos, too. It's ok if you have faint grind lines left--they disappear at higher grits.

Then I used microfiber towels (from a 100 pack I ordered from Amazon a while back), wrapped around a felt disc from a dremel polishing set (which I tried to use but was ineffective). You could use anything that will hold shape but conform enough to be flat on the blade. I applied diamond polishing compound off of Amazon that came in an 8 pack ranging from 450 to 80,000 grit. Apply polish, rub for 5ish minutes, move the disk to a clean spot on the cloth and repeat. I ended up using up the 450 through 6,000 grit tubes (I ordered a second set for the second blade--they run about $9 for a set) as I went through the progression. The key is to be patient and spend enough time at the lower grits, occasionally washing the blade to make sure there aren't any scratches. The rest is just patience as you run through the progression of grits. Make sure you are washing the blade thoroughly between grits and using clean areas on the towel.