Premium services
You can charge extra fee for the premium services that you charge.  In addition to all the free services that you provide, premium members get additional services such as image hosting, add free petitions etc.

Donations
Most of the times people are ready to donate a decent sum to the petition hosts. In order to en cash the same you can place Paypal or EGold donation buttons there. Even if the donation is small, it is still an added income for your site.

Legal notice
It is essential that you have a legal notice. It is absolutely necessary that you have disclaimer that states that any petition that is posted on your site dose not in any way reflects the opinion of the firm or the paid sponsors.

Promise privacy
It is important that you specify that you so not share or sell the personal information such as the name and the email addresses of the petitioners that is included in the petition.

Tell a friend tab
In case you  have a tell a friend tab, that allows a person to forward a petition to his friend, then make sure that you do not store the email address of the friend on your data base.

Petition topics
You can write a petition on any serious topic that demands attention; it could be any topic such as lifting UN restriction.

Well written petitions
It is very important that the petitions are well written, because a well written petition can attract a lot of attention including media attention.

The extra effect
You can add photos related to the petition for the extra effect.

Mention your details
Specify your name and address in the petition.

Positive petitions
Do not accept any petition that promotes hatred and ill will.