You say that you have a domain selected and site built. If you properly built these with ' a theme and purpose ' in mind for what your membership service is about, you already have your answer as to what to promote to your members.
As for how, you should post an area, where the members seek these offers out, in a ********* section of your membership site or forums.
Furthermore, you should use email/newsletter and properly present your offers of the week in a newsletter that they expect to open and read, never flooding their inboxes with 10 emails per day of junk, which they will never open and read.
Give them a simple, SINGLE email per week and give them a link within it back to a webpage, where you give them your newsletter of content and have ad boxes and banners rotating in the sidebars and footers. If they see something they like, they will click it.
Don't force ads on them...they will unsubscribe from your email list, as well as your site if you fail to provide value. You also have to ' present the oppertunity for them to click on what they are interested in from your offerings ', not flood/annoy them right off your list. Guru do this same technique all the time by flooding email accounts with every little thought that passes their tiny, greedy little minds and within a month, no one reads them unless they are giving something away for free.
Don't be like them. Be smart and keep your members longer than anyone expects. The average email lister for a guru is 2-6 WEEKS of lifespan before they go cold. I habitually keep members on my lists for a 2 year min., only losing them to a change in lifestyle not needing what I offer at that service anymore. The funny thing is that it is only a technical loss, as 98% of the time, they move from one membership to another in my network, giving me another cycle with them that last for even longer than the last.
Bottom line: You have to offer your members what they expect from your membership...to know what to offer is already there, in why they joined your membership in the first place...for the themed purpose of the target niche market it is presented within.
Hope this helps.