I'm a passive seller. I buy good keyword .com/keyword brandable .com domains and wait for the end user to initiate contact. I list at Sedo, Afternic, and DomainNameSales but most of my leads/sales come direct from my own sales landers contact form as all of my domains for sale redirect to them. So I....
1) Buy domains that make business sense
2) Forward to my own sales lander
3) List at Sedo, Afternic, DomainNameSales for additional exposure
I have enough developed sites to keep me busy and not become impatient on leads. I'll wait years for the right buyer over a quick flip as I prefer a hand reg turning into x,xxx-xx,xxx over hand reg into $20 since holding costs are only $8 and some change a year. Since GoDaddy bought Afternic that definitely adds them to a must do as it puts all of your domains into the registration path at Godaddy and GoDaddy has the most end users due to being basically the only site you see doing massive TV advertising. Lot of people dislike GoDaddy but their basically the only ones reeling in end users with their advertising, don't see any Sedo commercials on my TV.