General hints
A nice photo will make your profile much more appealing.
Do not narrow down too much the choice of countries.

Hints for au pairs
Describe yourself. Which are your strong points and your weak points?
How do you imagine living together with your host family? Do you prefer a close familiar contact? Or do you want to be rather independant during your spare time?
Which kind of work are you willing to do? Children of which age do you want to look after?
You should preferably write in the language of the country where you would like to go. Even though your knowledge of the language might not yet be perfect. For you want to become an au pair to improve your language skills. You can also write the text in different languages one below the other.

Hints for families
Simple texts can also be read by au pairs who do not have perfect knowledge of the language.
If you speak the native language of the au pair, you can additionally write your personal texts ("Dear au pair" etc.) in this language.

How do you imagine living together with the au pair? Do you prefer a close familiar contact? Or do you want the au pair to be rather independant during her free time? When are the working hours? When will the au pair have spare time? Which work will the au pair mainly have to do?
How will the au pair be accommodated? Will he/she have the opportunity of attending a language course? How and where can the au pair reach discos, shopping facilities cinemas etc.?

Try to put yourself in the place of a 20 year old person. A nice house in the country may be something wonderful for you, but for a young person it might be unattractive.