Seo work for classified sites are more difficult because this type site have covered large area for working. This have many category and region for working. So you start with site category. Good Luck.
You must select the proper category for your site and go to the classified site, select the proper category,subcategory and finally submit your advertise there.
Seo for classified sites are same as other sites. Try to do better link building. Go for google adwords. Submit Articles. Do blog Commenting. Do link exchange with other classified sites. That's enough.
For classified site forum posting-a method of SEO is best in my sense. Only doing forum posting will increase your blacklinks but you will not get sufficient visitors. So I suggest you to use a SEO whole package software which contains all SEO methods. I have make a search on google and found a SEO package software named SEO Elite. I guess this software will make money for you within a very short time. Thanks
here i see many post about dont want to use software then google punish you...so i don't prefer software