Appropriate variety of sand sifting crews/detritus eaters/and general clean up crew. That coulped with sufficeint flow and proper tank maintance shouldkeep the sandbed looking good. (it's not ever going to be pristine clean like brand new dry sand, don't expect this, and if it does stay like that, somethings wrong.)
Yes, a cleanup crew will help. I prefer nassarius and cerith snails for the sandbed. Like papa said, proper flow is crucial. At least 20x turnover is recommended in the display. I have 30x in my 40g mixed reef.
Agree with the posts above --- nice looking sand comes with tank stability & clean up -- in addition to the snails, pods and tiny worms that live in your sb will do the job - something to consider in choosing fish and other tank inhabitants