Best way to clean iMac speakers

They need cleaning?

 

Never looked, although the speakers on the iMac are crap so I hooked up some external ones.

I presume you could just use a can of compressed air although that might not be recommended as you might damage them.

Try here and see what Apple recommend (if anything):

http://support.apple.com/kb/ht3226

 

I hear on the dust. This machine collects dust like crazy. When I put some extra ram in my machine, I had it face down on the bed and gave it a puff of air and could not believe how much dust I got out. I use a bulb blower since it's pretty gentle.
Power down, unplug, face down and remove the ram door. Then use a bulb or canned air to get the dust out.

 

Although I recently read that it was not a good idea due to static discharge, I've always used a regular vacuum cleaner to suck the dust out of any grillwork on my computers.

 

I would vac the bottom first and then use compressed air from the rear vent area downward. Blowing from the bottom will move some of the dust upward inside. Perhaps blow around the bottom after the first 2 steps.