You mainly get Brownie Points by giving items to the Big Cheese. The Brownie Points listed on the Players Page come from these donations.

However, you also have some "hidden" Brownie Points that contribute to your Rank. Every dollar you have adds one Brownie Points, and the Brownie Point total of items in your Warehouse also counts.

Note that you do not get any bonus for Favored Attributes of items in your warehouse. You have to give them to the Big Cheese to get that bonus.