Answer:
there are several ways, you always start with having a shower, get a hair voluming shampoo or conditioner, but it doesn't really matter, if you can't get them.
FIRST METHOD
blow dry your hair and start sectioning it, piece by piece take your hair hold it upright, and spray your favourite hairstyle holding spray on the roots, keep your hair upright for a few second then let it drop work your way through your the part of your hair that you want voluminous.
(THERE IS A VIDEO ON YOUTUBE THAT ILLUSTRATES THE METHOD)
SECOND METHOD
don't blow dry your hair, put it in large curlers at the roots either spray style-holding spray, or apply gel or moose, wait till your hair dries and remove the curlers, carefully brush your hair so you don't flatten it again, and voila voluminous hair.