Null-Entity says:

It depends on the shot/character (I have not done many characters yet) but for my "Gent's Last Act" set I imagined an entire scenario with scenes, and simply played it out from start to finish in-front of the camera.

As for shots with Tasastock, it was a matter of thinking of the theme and playing along with it, it helped a lot to play off her!.

kirilee says:

If you are wearing a costume, think about where the character wearing the outfit may have come from? Some things to consider:
- Are they rich or poor?
- Are they delicate or tough?
- What social class are they from?
- What type of other characters do they hang around with?
- What is their favourite food/ drink/ past time?
- What would their voice sound like if they were upset/happy?
- Are they outgoing or more withdrawn?
- What is their more accomplished skill?
- Are they in conflict with someone/ something?
Etc. Etc.
If you find it difficult to get into character - try writing the answers down to these questions and even some more. This will help you not only to define your character, but get you thinking about how a certain character may hold themselves.

Tasastock says:

A little hard for me to explain, because I just kinda, do... But once you have thought up a character for your stock shoot, imagine their story. Who are they? A fighter? A lover? A coward? What kind of situations would they land themselves in? A battle? (Which you can then do a lot of fighting poses, imagine yourself in a fight, killing, being killed, down on the ground about to be killed, kicking arse, getting your arse kicked. Hiding behind a shield, firing at your enemy screaming with reckless abandon) or are they a wily hunter? that way you can do a load of stealth poses, tracking, crawling, crouching, climbing. What kind of moods do you want your character to be shown in? (The more variety the better) What has happened to them? are they sad? angry?
Make up a story for them, a long story. That way you can go through lots of different scenarios to create lots of different poses. Example: they were tracking a villian, found them, started to fight them, kick arse. All because they wanted to rescue their friend/lover, but arrived too late! oh noeeesssss the soooooorrrowww!!

Null-Entity says:

With practice... I am still trying to get there myself but it's all about looking at yourself objectively, ignore (or lightly fix) any flaws and look at form/shape/pose, try not to see the image as you but instead shoot for the best image you can create with you as a tool....

It will just take (and it's taking me) time.

kirilee says:

MUSIC! I try to drown out the fact that I am a regular woman, in a crazy costume, with soft box lights right near my face, and there is a timer on my camera that I need to strike a pose before it goes off. It can all be very stressful if you don't relax into it and accept that you are not a regular woman in a costume in front of lights and camera, you are a mythical character about to do battle with a great beast.
It takes practice, but pushing all the "doubting" thoughts out of your head is the key. Banish all thoughts of "Does this make my stomach look huge?", "Do I look like a complete idiot?", "If I pull a face I will look like a cat who just ate a lemon!" - it doesn't matter. That is the joy about digital cameras - you can review after and put only the best ones up.

Tasastock says:

This is harder to do, but if you're imagining a character this shouldn't be as bad. Anyone of you who has me on facebook miiight have noticed that in ordinary pictures of me, I am constantly pulling a silly face, (and/or drunk... but enough about that) because I can't take serious photos that are of me. But when I am shooting stock, it's not photos of me that I'm shooting, it's of whatever character I am choosing to portray. (If that makes any sense at all. I may just have lost the majority of you somewhere. Well run to jump back on the bus ladies! We haven't got all day)
Think of making up a character for your shoot almost like an alter ego. Immerse yourself in what is happening to them, how they would hold themselves, what they would do, react, how they express themselves. Because, you yourself can't be embarrassed about these things, because you're not you, you see? (That's very Alice in Wonderland logic but it so works) Just remember, there is no point being scared of taking a photograph, if it doesn't work and turn out the way you want it, that's a lesson learned and you tried. Even if you're not entirely happy with one aspect of your photo, but could see it being really useful for artists, upload it anyway. The more variety you have in your gallery, the more likely it is that your stock will be useful to someone. If it's self-consciousness you're struggling with: remember what you think about when you're looking for stock photos yourself. You're not looking how someone is dressed or the shape of their nose or their haircut or anything silly like that. They are looking for the pose. They won't be looking at you in that way at all, when you are drawing someone they become angles and shapes and lines. Very analytical, and not at all personal anymore. (That line of thought, is how I do nude shoots, btw. )

Null-Entity says:

I cannot speak for using a professional photographer, my only experience is with friends, quite simply have fun, make jokes and work as a team, it's not about you and them it’s about "us"....You won’t get a good picture without them and no matter how good they are they won’t get one without your help and input.

As for a 3rd party not involved in the shoot I think it would be a matter of simply ignoring them and concentrating on your shooting.

Time and patience and a little bit of fear I would imagine (I have a long way to go).

kirilee says:

Tricky - I suggest you start with either a very good friend who you know won't judge, another stocker who won't judge..... or a complete stranger who you don't care if they judge
The most important person that needs to stop judging you though is always yourself. Trust in yourself and go - have fun and play. The other person there will take photos and should bounce off as much energy as you give them.

Tasastock says:

Getting to know them first helps. I find that I'm a bit of a prat the first time I meet people, mainly cause I'm so excited about meeting them that I can't sit still and concentrate on photos. So if you've never met them before, a prior meeting will help. If it's your friend or something, then you've probably been acting like silly-beggars around each other for so long that it shouldn't be a problem at all. No one is going to judge you for modelling. It might look a little odd out of context, but as soon as someone sees the photos, it all comes into context, whoever is behind the camera should be busy concentrating on getting the shot right. So don't worry about them, worry about what pose you want to do next

Null-Entity says:

Have fun, make jokes, mess about and then get serious. If you are not having fun.. why are you shooting?

kirilee says:

Never take yourself too seriously. If you ever feel like you are getting caught doing the same thing over and over again - switch it up. Try reacting to these suggestions as your character:
- Sitting/ crouching/ jumping/ standing/ turned to the back etc.
- Grab an appropriate prop and incorporate that
- "OH! Something big is coming at me!"
- "Why is there suddenly all this mist?"
- "It has been 2 hours.... where is he?"
- "Something fluffy is bouncing towards me!"
- "You have to be kidding me..."
- "Be quiet!"
- "Must.... not.... kill"
- Your lover has just left you
- You see you childhood home in flames
- You outwitted a foe

Tasastock says:

Music. Music helps a hell of a lot, different types of music will help you envision different scenarios, give you different ideas, and help you portray different moods. Heavy metal music helps me do the angry, snarly screaming shots. Quieter music helps me do shots where I'm trying to portray sadness or depression.
Also, look around the stock gallery to see what others have been doing, and try to think of what is missing. Some groups have pose request lists (I know ManStock does) so have a look at what some people say is needed or wanted. Make a list of very particular poses/scenes that you want to do, so that you don't forget. Try and get different props as well, to give your character an arsenal of things to play with, which will also help you generate different poses. Even something as simple as a book, or glass.