Here are some few tips to make paper from old scrap paper :

• You can use cardboard, newspaper, old books, tissue paper, magazines, junk mail, typing paper, construction paper, unused napkins, old toilet paper rolls, and just about any other kind of unwaxed paper for this project.
• Newspaper, tissue paper, and some other types of paper (like magazines) may alter the color of your paper (i.e., newspaper will give your finished paper a grayish cast).
• For extra interest, you can add small bits of unblendered paper to your pulp; I’ve had success adding small torn-up bits of an old book to smooth pulp to make interesting envelopes out of my paper. You can also add other inclusions, like bits of string or flower petals, to your smooth pulp.
• If you plan to write on your paper, you might want to add some liquid starch (two or three teaspoons) to your pulp mixture for sizing. You can also use white glue, if you don’t have liquid starch.
• Your paper will be in the size and shape of your mold and deckle. You can make a mold and deckle with two picture frames (without the glass and backing) and some window screening: staple window screening to the outside edge of one picture frame to make your mold. Make sure the screening is taut across the frame. Fiberglass (as opposed to metal) screening works best. Trim excess screening from edges of the frame. Use a frame of the same size as your mold for your deckle.
• You can also make a mold out of a can - coffee can, bean can, whatever. Stretch your screening across the mouth of the can to make your mold and tack or staple it to the side of the can. Embroidery hoops can also be used to make a mold and deckle, in the same manner as the picture frame mold and deckle.
• You can buy a mold and deckle from a papermaker supplier, and from some craft stores.
• The cloth you couch your wet paper sheets onto will affect the finished look of your paper. Colored cloth may bleed color into your paper; if you use a towel, one side of your paper will be textured like the towel.
• Most homes, these days, have a paper shredder. Using the shredded paper will save the step of tearing the paper into 1 inch squares.
• Gel or liquid inks will not hold to written lines on this sort of paper (the ink spreads like water on a paper towel) unless you treat the paper. Once it’s completely dry, brush it all over with a solution of gelatin and water and let it dry again.

(source : wikihow.com)