You might find the New to Mandalas thread of interest.
Here are basic guidelines from posts written by @_OM:
But how do you wear it exactly?
So, you can print it out. Color or Black/White.
Resize it HOWEVER you want ie. pocket sized.
Old school people will laminate it and either put it in their pocket
or
you could use a punch hole, a necklace,
and throw it around your neck (this gets itchy)

Can I make it into a poster for my room?
Yes.
Edit: Any size is effective. Note that the effects can become stronger the larger the mandala is. Some may find larger mandalas overwhelming.