MadFish wrote:
Concentrate on providing good quality content or a useful service, and update your site frequently. Try to encourage community participation if you can.
MadFish hit the nail on the head. No matter what you do to build a revenue stream on your site, you have to be able to draw people to the site. The key element here is to figure out what value your site adds to your customer.
Portals -- XOOPS is a portal-builder after all -- offer value through a confluence of content, community and commerce. If you are providing content of value then you need to make sure that you are delivery content that is of good quality and that is updated frequently. If part of your model is the community that forms around your site then you need to make sure that community is actively engaged. And don't forget the opportunity to engage in commerce. Your business may not look like an e-commerce shop, but there are always opportunity to sell goods and services to your customers. Subscription models for premium content depend on...well... premium content.
Regardless of the focus of your site, you need to be actively marketing it. People who aren't customers now need to know that they can be customers. And that involves, as was mentioned above, posting actively in message boards and groups that relate to topics of interest to your customers. If you know who they are and what problems they are trying to solve then you should be able to find the places that they frequent and get your message across.