In answer to your sig: underwater :wink:
Time and patience are the easiest and best was to increase the population of critters in your sand bed. Feeding 'more' could work, but I think one should feed a tank as much as one can, while keeping equilibrium with the system and the means of nutrient export(critters, filtration, etc.) Usually enough uneaten food/feces gets to the bottom of the tank to sustain and grow the population without you having to actively feed the DSB(except during a cycling of a new bed, in which case I encourage feeding the bed, with say flake food...)
One sure way to increase sand popoulation is to exclude anything that feeds on organisms there- this includes any sand sifting gobies, etc. that sift the sand for critters- all day long. In my opinion, unless you have a very large tank, it is best to exclude these fish. Pod eating fish should also only be added to large tanks(mandarins, most wrasses, dottyback, etc.) Cukes and stars general feed on bacteria and detritus, and are good stirrers...
Hope this helps