To make $100 a week what you need is well maintained Blog, Huge Traffic, and useful and original content.
Lets first focus on traffic.The more traffic you have the more you can earn.you need to follow so basic steps in order to achieve your target of $100 a week.
1. Always write original content for your site. Do not try to copy content from other blogs or website.
This is the biggest mistake most of the new webmasters make.
2. Submit Your same(Original) content to Article Directories in order to get good quality backlinks.
3. Keep responding to your visitor;s comments and suggestions.Doing this will build good relationship between you and your readers.Your visitors are the important asset for your website.
4. Adopt one good quality backlink building strategy for instance Forum posting,Email signature,Blog commenting etc
5. Keep repeating above steps untils and unless you reach the goal hundred visitors a day and $100 a week.
One you are done with good blog and traffic you can also start other services on your blog in order to increase your earnings like clickBank, Amazon Affiliates and many other affiliate programs.
you can also sell ad space on your website. This will also increase your revenue. but for this first you have to create a good blog and traffic to your blog.