heres something i learned taking a graphic art and design course in high school. you can apply these same principles to your graffiti aswell. in fact i'd suggest it. these apply to things like sign making and ads for the yellowpages.. but its a principle..
remember..CRAP.. yes crap.. Contrast, Repetition, Alignment, and Proximity. in short.. crap.
Contrast
The concept of contrast says that if two items aren't the same, make them very different. Contrast adds visual interest to your page. You can create visual interest by using color (as in the banner portion of this page contrasted with the content space), size and weight (as in the contrast between the headings and the paragraphs in font and weight), or any other property of an element. Again, you can utilize style sheets to make this easier by setting contrasting values for heading font and paragraph font.
Repetition
The concept of repetition says that you repeat design elements throughout the entire piece. The element can be a font style, graphic, line, icons, colors, the list is endless. The web makes this easy to do in several ways. First there are style sheets, which allow you to set elements of a web page to certain fonts, colors, locations on the screen, etc. It is fairly easy, and I recommend you copy my stylesheet, just to see what one looks like. If nothing else, add the style information for "A:Hover", it will makes links change color when the user mouses over them. You can also view the source of this web page to see how I linked up to the stylesheet.
Alignment
The concept of alignment says that everything on a page should be visually connected to something else on the page. Nothing should be placed arbitrarily. When elements are aligned they are connected to each other, even if they are separated on the page. You may have noticed that the alignment of the subheading "Alignment" was centered. As it is said, "Good design is transparent." The lack of alignment between the subhead and the related paragraph made your eye have to travel across the page, and it was probably enough for you to notice.
Proximity
The concept of proximity says that related items should be grouped together. Likewise, items that are not related should not be close to each other. The process of grouping related information creates visual cues, which accomplishes Jakob's principle of facilitating scanning. An example of proximity is the relationship between subheading for my paragraphs (such as Proximity above), and the Paragraphs below them. Williams also suggests never having the same amount of white space between elements that aren't a part of a list.
also,
http://www.mundidesign.com/presentation/index2.html can help.
if theres any questions i'm sure i can help answer them..