While I don't get a lot of people contacting me, I find a large number of the ones that do are seeking a Domme and ask me about how to find one.
There are a couple of common characteristics I have found with these subs:
1. They have little to no real life D/s experience (that they haven't paid money for).
2. They have allowed their fantasies and fetishes to become over-developed before pursuing the lifestyle.
#1 is no big deal to me, everyone has to start somewhere, but #2 is crawling with problems.
As subs, especially before we have taken the plunge into the lifestyle there's usually a fairly long transitional process as we develop into submissives. It usually follows some sort of cycle of being very turned on by a non-traditional means and fantasizing about it, feeling fucked up about it and trying to make it go away, and after several iterations of the first two, finally coming to acceptance that this is something we don't want to live without.
If this process takes too long and is too intense (often assisted by fantasy-based fetish fiction) there's a tendency to develop a romanticized view of the D/s lifestyle and what their role will be within it, complete with theatrics and their perfect fantasy Domme. I generally try to steer them towards my tips for courting a Domme but this often falls on deaf ears (or blind eyes).
All subs would love to have this fantasy life. Those of us within the lifestyle have usually developed more reasonable expectations of it or managed to learn to crave what She enjoys. In this way subs that have a fetish for domestic servitude and performing unsupervised chores have a leg up on the competition (a whip-cracking task-Mistress standing over you while you clean the toilet isn't a reasonable expectation). Subs that have a thing for suffering on any level (mental, physical, emotional, sexual) are also pretty well-suited for the lifestyle although it can be difficult to find a demanding/cruel enough Domme to be a good fit.
Overall, there's a word for subs that have to have things the way they are in their fantasies: single. If it doesn't do anything for her, she probably won't do it. If you are out seeking a D/s relationship the best advice I can give is to try to keep your fantasies in check and make an effort to steer them towards things that make sense for her:
She will probably enjoy hurting you physically (without causing permanent damage).
She will probably want you to worship her body.
She will probably want you to perform domestic tasks.
She will probably want to do some tease & denial but she will probably expect your penis to perform for intercourse as well.
Assuming you are seeking a loving relationship, the above characteristics are probably a fairly safe assumption to make. For most things beyond that (chastity, feminization, pegging, torture, branding, etc.) it really becomes hit or miss and that is more of a good fit/bad fit situation.
It's not sexy, but fantasizing about yourself as someone worth talking to and being with is far more beneficial to your cause than fantasizing about being a naked slave sleeping outdoors in chains in a pile of your own feces unless you end up finding a Domme that wants to have an unemployed slave that doesn't really contribute to her personal life.