Tags are an artists signature piece of graffiti, usually a stylized depiction of the artist's moniker usually drawn in marker in a blackbook. New artists will master their tag in a blackbook drawing it even hundreds of times to master the letters and the ornamentation. The art of the tag is much more about style and movement than it is about legibility, and tags that are too plain are considered sub-par by those in the street art community. The blackbook allows artists to master their tags at home before putting them up.
Throw ups are relatively simple works of graffiti, sometimes of the artist's moniker but other times of a clever word or phrase. By definition, a throw up is a two-color composition. Because there are only two colors in a throw up, choosing them is a very important part of the process. A blackbook allows an artist to try out different designs and color combinations of a throw up before she even buys paint. She can keep the different designs to refer back to when she finds a good wall to bomb.
Pieces are complicated works of graffiti usually featuring three or more colors of paint. Because of their elaborate nature, they take a good deal of planning and color coordination ahead of time. Blackbooks are excellent places for graffiti artists to work out the details of the piece before they have to execute on a wall. Artists can keep plans for future pieces in their blackbooks. That way, they can keep track of their ideas even when they don't have the time or the wall to put them on.
Many times, graffiti will feature a character of some sort. Sometimes they are cartoonish, other times they are realistic. Often they are used in concert with a clever or satirical word or phrase. Graffiti artists will develop their characters in blackbooks, and the same character might make an appearance in several different pieces, though often in different poses or with different words. Blackbooks allow the artist to brainstorm and create variations on his character theme.
Artists use stencils in graffiti because they make painting complicated images faster and easier. Oftentimes, stencils borrow images from other media, such as magazine or newspaper photos, and alter them for meaningful or humorous purposes. Stencil artists will include cutting and pasting of many of these images in their blackbooks with accompanying sketches or words. Keeping close track of found images is an important part of stencil street art.