If you're just starting out in the BDSM scene or as a bottom/submissive/slave, you may not be sure where to start. You have these desires, but are not sure how to realize them. You may have a significant other, but are afraid to tell them. You may be unpaired and are unsure where to start looking for someone to pinch your nipples, slap your ass, and then set you on fire...that sort of thing isn't in the yellow pages. So you take to the internet and start wading through the sea of Dommes, Mistresses, and Goddesses. How, among all these intoxicating creatures, can you possibly ascertain which person will sate your curiosities?
The first step is to look within. You will need to do a little soul searching to establish just what sort of scene you're hoping to enact during a session as this will point you in the right direction in your search. Seeking blindly won't get you far, and if you make contact while clueless, you may well be disappointed. We won't dominate you over email or via phone attempting to figure you out, and it's extremely selfish to expect Us to.
Now that you know what you want, make sure that your interests seem to align with the type of Domme you're looking at. If you're into wearing diapers you probably don't go looking for a Princess.
She's an animal trainer, but do you really wish to be a human pup?
You want to be pegged, but She also demands that you be locked in chastity and dressed as a sissy. Is that something you're into, or a deal breaker?
You're more of a fetishist but She's a female supremacist who demands submission. Those sorts of pairings may not work.
Some Dommes have more than one persona that they play with; the Sadist, the Goddess, the Governess, etc. Diversity is not a bad thing and doesn't make Her any less qualified in each area.
Next, do your due diligence--research! Studying a potential new Domme will aid you in a myriad of ways such as gleaning insight as to Her personality and what kinks She services (also how to get on her good side). Most likely there are pictures of Her working, or of Her handiwork, if not a list of Her specialties. If you read Her writing, you can probably determine Her true voice to get a feel for what sort of person you'll be interacting with--strict, benevolent, nurturing. This is no replacement for actually talking to Her, but may give you a general idea if you'd like to pursue speaking with Her.
Now, see if She's established. Investigating will quell any fears about being abused or taken advantage of by someone trying to make a quick buck.
Do they have a web presence? For how long?
Are there people who follow them?
Do they interact with others?
If the answer is 'yes' then they are likely trustworthy. People in the community who are unethical become isolated quickly and don't stay long.
Finally, you can think about making contact. Meeting with a Mistress is still entering a relationship of sorts, and should be treated as such. No, you're not dating by any means, but both parties have needs to be respected. Negotiation is an important part of initial contact--have an idea of what your needs are versus what She can provide. It is disrespectful to contact someone knowing that one of your strong desires is against their hard limits--inevitably, this would be a waste of time on both your parts. At the end of the conversation, always make sure to thank the Domme for Her time.
Be prepared for rejection. Just because everything looks good on paper, that does not mean your personalities will mesh. If you're polite, She may have a recommendation for you to find what you seek.