You make money when you sell your products and services.
You do not make money just by posting ad in itself.

So just posting ads alone is not enough. You need something to promote and sell.

Below are some suggested affiliate programs which are free to join and that you can promote on The Free Ad Forum:

Classifiedsubmissions.com Affiliate Program: 

Learn more and sign up here for free here: https://www.classifiedsubmissions.com/affiliate-program

This program is free to join and pays 50% recurring commissions on all sales. This is a hot seller! We have sold thousands of these membership.

What better service to sell to people coming to post ads on classified ad sites than a classified ad posting service? We have sold 1000's of these memberships!

You can get banners, sales, letters and promotional material here: https://www.classifiedsubmissions.com/affiliate-tools/

You can get a free re-brandable ebook which re-brands instantly with your affiliate ids here: https://www.classifiedsubmissions.com/freeebook

Re-brand this ebook with your affiliate links for Classifiedsubmissions.com and Coolmarketingsoftware.com and if anybody orders you receive 50% commissions.

Coolmarketingsoftware.com Affiliate Program.

Learn more and sign up for free here: https://www.coolmarketingsoftware.com/affiliate-program

This site sells marketing and classified ad submission software. You earn 50% commissions. There is also free software available. 

You can give away the free software and if people upgrade to pro versions later you earn 50% commissions.

You can get banners and promotional material here: https://www.coolmarketingsoftware.com/affiliate-tools

Realppvtraffic.com Affiliate Program.

Google makes all of it's money selling traffic. If you just get a fraction of that market you can do pretty well. This site sells traffic.
You earn 30% recurring commissions on all sales referred.

Learn more and sign up for free here: https://www.realppvtraffic.com/affiliate-program
Promo material here: https://www.realppvtraffic.com/affiliate-tools/

The above affiliate programs are just suggestions, you are free to promote any legal, moral and ethical products and services you wish

Here are some more affiliate tips for those serious about affiliate marketing.