"What advice would you give to someone just entering this lifestyle?"
Ooh geez, lots. Lol. I suggest coffee. Maybe more than one cup. This is likely to get long-winded and out of hand.
I guess that first and foremost, it would be not to care too much about how other people do it. I know that this might make the rest of my thoughts kind of a moot point, but...
In the beginning, its really easy to get caught up in "The right way", which is usually just modeled off of what we have read and seen--because not having our own past experiences to rely on, we look to the experience of others. Now don't get me wrong, there's definitely something to be said for
It can be awfully difficult to remember that what we read is a snapshot--a picture of a moment in time or a thought process shared by the writer. Not everyone is willing to dump their mistakes and bad days out onto the internet for consumption by the general public. So before you decide that your brand of D/s sucks monkey butts, (sometimes it will. Promise--happens to all of us) remind yourself that people tend to share the times of smooth sailing quite a bit more often than they highlight the choppy seas.
Be honest. Be honest with yourself, and be honest with your partner. If you're not honest with yourself, you can't be honest with them. And if you're not honest with them, you either aren't going to make it very far down this road, or you are going to put yourself in a situation where you get hurt because the other person doesn't have enough pieces of the puzzle to help put you back together if things go awry.
Take it slow--the world is not going to end because you didn't do/get/experience it all yesterday. Seriously. Take your time. Chances are, you won't be dying tomorrow, and it is far better to work your way slowly towards something wonderful than it is to rush headlong into a disaster of your own making. You cannot go back and undo what has been done, but you can give it a damn fine go the first time around if you move slowly enough to do so.
Blanket advice aside, I admit that I would probably give Dominants a little bit different advice than I would to a submissive. Because yea, different ends of the power spectrum.
To a Dominant, I would say remember that you are not omnipotent. There will no doubt be times when you will feel that way, and your submissive will certainly view you that way more often than not, but...In the grand scheme of things, you are not.
You will make mistakes--to err is human, and you are still human. What really matters is what you do with your mistakes. Own them, admit that you were wrong, don't repeat them, and if warranted, don't be afraid to apologize for them.
If you want your sub to live up to your expectations, you have to give her the tools to do so, and accept that you must both work within the rules of reality. For instance, you can't expect to be met naked at the door every day if there are kids in the house. It's just not feasible. The examples could be many, but it boils down to the fact that you cannot expect someone to submit to you if you are unwilling to do some work for it and adapt to the constraints of life in general.
Be consistent. Seriously, I can't stress this one enough. Consistency earns respect and provides a submissive the framework within which to exist. You can't expect anyone to do what you tell them to if your expectations and the consequences of their actions are inconsistent. Plus, we're finicky creatures and consistency makes us feel special and stable. It shows us that you care.
Let her feel what she feels, and share how she feels. You are working your way through the inside of a human mind with a heart attached. If you want unfettered access, your sub has to know without a doubt that she can tell you anything--otherwise you'll never make it past the outer walls of her mind. If she can't share the most twisted, darkest, angriest, saddest, parts of herself, you won't ever truly own her.
If you want her body to be your playground, you have to get through her mind first. Wonderful and terrible things can happen to the human body and never touch the mind, never reach the soul, never impact the heart. If you want to well and truly own another being, you aren't going to get there through what you do to their body alone. If you can touch her mind, she is more yours than touching her body could ever make her be.
That's not to say that the two don't often go hand-in-hand, but they are not certainly not mutually exclusive.
And lastly? Yea...It's pretty simple--just don't be an asshole.
To a submissive I would say, remember that he's human too. At the core of ourselves, we're all just human beings being human. Yes, you are putting your life in the hands of a mere mortal. There are consequences to that, and they aren't always pretty. Accept it. Get over it. Don't hold his mistakes over his head.
Don't push him to do things your way. While it is important to acknowledge and be honest about your needs and wants, D/s is intrinsically not about getting your way--it's about doing things his way, having the faith to trust someone else to make the right call, and the wherewithal to suck it up when a call you disagree with is made.
Don't expect him to be Dominant if you are busy running around questioning every decision he makes--Domination becomes ridiculously more complicated and difficult when it's constantly being challenged.
Really, expectation in general is not your friend--it makes us too caught up in how we think things should be as opposed to living how he thinks we should. If we are always too busy with our own expectations, there isn't room for his. And, after all, D/s isn't really about what we want.
If you want him to know what makes you tick, what really and take advantage of it, you have to let down the walls. Let him in. Not the superficial way we let people in, that's not going to get him there. But the way your skeletons know you--the scars that make you who you are, the things that are hard to love about yourself, the desires you hate admitting to yourself.
Submit. Sounds pretty basic, kind of like not being an asshole, right? But it's not always so simple. D/s is a cyclical reciprocal arrangement, and if you want Domination, you must offer submission. It's easy to submit to the things we want, not so easy when every bone in our body is screaming about how badly we don't want to do it. I think that, quite often, submission is very much about the things you don't want to do. And doing them anyways.
I'm sure that I'll think of a million more things tonight at midnight, but there you have it.