Its a long and difficult process. Most Dommes are inundated with potential subs and most of them are not (in their opinion) worth bothering with. There are a lot of wannabes and fakes and those who simply just want to find a Mistress for some quick, dirty sex without any of the committment. So, the first step is to show that you are serious and committed to a lifestyle of service to a woman.

A personal ad may get you some notice but they rarely get answered. The best way to find a Mistress is to interact with the lifestyle in a positive manner. So, you need to post on the forums - asking and answering questions - to show that you are willing to engage in the issues of BDSM, including the ones that are not simply about sex. You need to go into chatrooms and talk to Dommes, subs and Doms in a way that shows you are not a dangerous stalker or a wannabe idiot. Interacting with people as human beings rather than charicatures is a good start. Definitely not walking into a chatroom and shouting 'I am looking for a Domme' as that gets you immediately on most Dommes' ignore lists.

The key is patience. Once Dommes know you as a friend they are more inclined to think of you as a potential sub.