That actually depends on her wishes, etc. My opinion is that being dominant or submissive, and being sweet or mean actually doesn't have much to do with each other. Well off course a submissive person is less likely to show the master some fangs, but on the other hand I believe that dominant may act very sweet and caring, yet still be demanding and strict enough. You don't have to be mean. You can punish her saying something like "Take it, that's what you get for disobeying me!!!" or, on the other hand something like "Oh, poor baby. But you'v brought it on yourself, didn't you? You'll have to take it now...". So here - the point is that you actually be very sweet, care about her, be romantic with her, give her presents and buy flowers, whisper things at her ear, while hugging her gently on a bench at the park... And yet be dominant, and be strict and decisive in your games or if she obeys rules. You don't have to change into a mean person to be dom. You'll hate it yourself in the first place.
Now, what to write in a contract is entirely up to you, and you should look at her and yours wishes on that matter. That actually depends from girl to girl very much. One would enjoy if you'd spank her to a hard tears if she screws. She'll cry on her knees, but she'll love the whole lifestyle. The other girl may hate it. One will feel submissive committing one type of activities, say, if you'll forbid her wearing underwear at all, the other wouldn't find that appealing at all. So this is up to her, and you should discuss her kinks and limits to find out what's best. Now...
How do you make your contract.
First of all, get a set of things that she will agree doing for you. You may very well find that out in a sexual play too. Say she doesn't mind some pain. Prepare a punishing session for her. Have her write (or tell you) the list of things what an ideal pet should be able to do. Then I personally would toss her a bit and punish her, and when she's getting quite enough, tell ehr that you aren't impressed with the list. Suggest a few things you would like her to do, and make her accept them by punishing her more (BUT note that any person has a forbidden list that he/she wouldn't like to do in any way or form - you should avoid it. Also every person has things she feels uneasy or afraid or shy about, that MAY be added in this list). Don't forget that your favorite kinks should be in the list too, or else that's not funny.
Make her suggest a few mote stuff she may be doing and so on. Decide what her punishments may be, make her suggest some. It should be something she doesn't enjoy or even afraid of, or else it's no punishments. If you will punish a pain slut with spanking - she may as well LIKE it, so what punishment will that be? Make it something pushing her limits, something she don't want to do for fun. Even if she likes pain a bit there's such pain she would hate. (BEWARE though, S&M is a dangerous life-threatening activity! You should always think twice and do only something that won't make damage to the body). There are actually a lot of things to punish a slave with. Pain, humiliation, housework, taking her entertainment away (a week without computer, if she likes it, or no friends meeting, or cancel a planned dinner with her, forbidding the favourite food, OF COURSE orgasm denial, etc), inconvenience application (make her sleep bound, wear anal plug the whole day, make her always go with one hand tied behind her back while at home, etc), or even the change of your attitude to her (less talkative, for example, however that's not for every relationship, I'm just throwing in the METHODS here).
Make it clear that the list is totally at her limits. Then I would say in your place that this is a list of perfect pet's qualities, but as she's obviously not qualify to it yet, you'll toss something away FOR NOW. Of course you can always change your mind or add something new - we are all humans, our views change...
Don't forget some routine, if she's into a pet thing. Make her clean the house daily or something like that. Also It would be a good idea to point out that as a pet she will have sex with you whenever you want and the way you want. So no "but i'm tired after work..." sort of thing. If she'll agree to it then - than stay true to it. Fuck her even if she's tired (However a dom's main concern is he's sub's health, so if she feels bad you probably should avoid it. If you have a relationship you'll probably always know when she's sick). Feel free to go shopping with her or buy her sexy outfits (only get her measurements first) or even toys, feel free to ask her to wear whatever outfit you want for her.
Well' there's simply too much things. I suggest you reading female subs forums for the ideas - they often share their experiences there, like what they were made to do, reviews on some activities etc.
Now you'll probably be able to create a contract.
A few more advises:
1) never pity her in the aspect of punishments. If you'v decided on 50 ass spanks, make them all, make them hard, even if she's "really-really sorry" or is crying on you. SHE wants this lifestyle. SHE feels really good about it, even if she's afreid of upcoming punishment NOW, she will feel unsatisfied and unfulfilled if you lust let it go, when she knew she deserved a punishment.
2) Never change your or hers personality. That's unnatural and will lead to the uneasyness and depression for one of you, because every man needs to be himself. Restrictions may apply on activities, but not on the behaviour. If she thinks you are too sweet - show her that a really great (and fearsome) dom may be controlling her with a loving smile on the face. There are fetishes of a dirty talk or mean behaviour, but they are actually really rare. what people always mix up is a dominant (egoistic) behaviour and mean attitude. While they actually want only someone dominating near them, not necessary mean. It's just that mean people are egoistic, and sweet are not. That's why they see where's the source of this egoism (dominance) and are driven to it.
3) Always check up on her. Make it a daily routine for both of you. Make her give you a daily report on what she did (especially your orders), who she met and what happened. Not just the sexual thing - all. What happened at work, etc. It's a good idea anyway, women like when men are interested in their day. You may also punish her if she screwed at work, and make her promice she'll be a good girl next time. That also takes her stress away - she doesn't feel that tense and bad about that mistake, also she feel your support at her work further on, like she don't just working, but working because you supervise her. Not JUST working, but working FOR YOU. That's a great support for women.
Better take those reports in person or at least by phone. Text messaging lacks emotion. Don't just listen to her. She should understand that it's her REPORT to you as a master, but you guide it like a normal conversation, joking, asking specifics, making comments...
4) A good idea to make her always have a reminder on her about you. I like the variant of collar worn 24/7. It shouldn't be a LEATHER collar or something that'll stand out too much. There are descreet things like a string of lace cloth around a neck. It's just for the look, but it is a reminder. Something like that:
http://darudar.org/var/files/img/e6/4d/ ... 58_600.jpg
They can be bought or even handmade. Wristbands are good too. Any way something she'll wear constantly (in a bed, in the shower, at work), something she'll see constantly (piercings are not good).... That's good IMHO
That's about all that comes to mind right now, I'll post more if I think something. If you would like specifics, like "how can you make her hurt without marks" or "How to humiliate her" etc - feel free to ask. There's a lot of people here who'll give you tons of specifics.