The most common way is putting Adsense or similar advertising programs on the home pages. Other ways include selling links or banners on the proxified pages. Another way people use is to create a mailing list, and then when loads of people sign up, sell blasts.
I have made a mailing list but I don't know which is the best tool to be used for it! Hotmail has limits! Can you suggest me a great tool!!^^Thanks!
Well, for proxies, Google and Yahoo groups are very successful and highly used. Basically, make a group (google is probably better as more people have a google account already) and then you'll get a code where people enter their email and are part of the group. Put this code on the home page (or proxified) and then say something about getting the latest proxies to your inbox, and people will subscribe!
You can earn it by various way for example by offering paid proxy which mean those people who want to use your proxy must pay you certain fee. Or You can make it free to use by putting some ads on it such as canep/adbrite etc