How to know what information is it necessary to provide in order to secure an audition
All auditions differ and they differ even more when you break it down to TV, Film, Theatre etc. There are no specific rules or forms to fill out in advance of an audition, but obviously the casting director/producer etc need to know who you are.
If you're applying for auditions then you more than likely have an online profile (on Casting Call Pro or Spotlight) and you have to fill out information to register with those.
You'll have given your name, it might be a stage name and that's fine - but choose your name and stick to it across all directories. People wont be able to find you if you have a different name on each different site or directory.
Other general information you will have filled out on your profile are things like hair colour, eye colour, height, weight - they're not integral to getting an audition, but if a casting director is specifically looking for someone with blonde hair, they can narrow their search and right away your name will come up.
Playing age. This will probably be listed on your profile and is pretty vital. Nobody is going to cast a 20 year old to play and 80 year old when they can just cast an 80 year old. If you try to your playing age too wide it could harm you in the long run.
Past credits. It helps to keep them in order - some people recommend having them in chronological order, some people say go for biggest credit at the top. It's probably best to find a mix between the two - if your biggest credit is 20 years old, it's probably not that big anymore.
If you're applying for a specific role, maybe on Casting Call Pro, you should provide a little information about your previous roles. Don't list your whole CV - that's already on your profile. Add one or two lines about the type of character and what production it was. Keep it tidy though - no more than 2 or 3 recent roles.
Contact details. These are obviously key - if you can't be contacted then you'll never get an audition. That means you have to check your email regularly as well! Some online directories have their own messaging system (like Casting Call Pro) which means you don't have to give out your details straight away - it's good because it's safe and secure. People like/need to work fast, so it might be an idea to include a mobile phone number or direct email address once they've made contact.
Also on your profile should be any special skills, accents or languages. But make sure you're good enough at them if you're asked in an audition - making stuff up here to try and get a role is just a waste of everybody's time. If a role is specifically looking for a skill that you're good at then you can mention it in your message when you apply for the role - again, keep it brief and tidy, Casting Directors don't have time to read an essay from every application.
Finally, head shots and showreels. It's a whole lot more appealing to a Casting Director if they can see what you look like before they spend time calling you in for an audition. Head shots shouldn't be a picture from a night out with your mates - if you've not got a professional photo then you don't look professional. Show reels aren't compulsory but shouldn't be shoddy quality. If you haven't got much work yet then you can film yourself - but take some time to plan it. Know what monologue/scene you're going to do and obviously practise your acting. Set the camera up somewhere safe and sturdy and it's advisable to have a relatively plain background and keep props to a minimum. If you've got the money and time, there are people that will record a basic showreel for you. You'll probably still get an audition without a showreel but not without a headshot!
Overall, it's common sense. People don't need your life story or your inside leg measurement - at least not until you've got the role and you're at a wardrobe fitting. They just need to know who you are, what you look like and how to get in contact with you.