Mark Making and Scribbling:
Mark making is a general term artists use to talk about all sorts of lines and the quality of line in a drawing. Mark making is important in doodle analysis, as it can tell a great deal about a person's state of mind. This can be put together with the content of the doodle.
Light or faint lines could variously be interpreted as tentative or sensitive. Is the artist afraid of makign a mistake? Medium weight lines suggest a balanced, confident personality. Heavy marks can indicate resolve, strength, and energy. Agression produces overly heavy lines, and the paper may be impressed or torn. Varied lines can indicate instability. But remember that lineweight is often used quite deliberately, particularly in pencil drawing, to create shading effects, which may have meaning in the context of the image, but not in themselves.
Repeated Lines and Patterns:
Repetition is a common feature of doodles that suggests a methodical, patient approach to tasks. Repetition also increases the significance of a particular motif.
Random, energetic scribbles can indicate a disordered mind, or may be simple space-filling as a product of boredom. Small vigorous scribbles made into a varigated pattern combine energy and impatience with a desire for structure.
Large, complex doodles that have grown almost organically across the page suggest a persistent nature, a love of design and a desire to express ideas. These doodles can sometimes indicate frustrated artistic ability, especially if ornate forms are embedded within them.
Some sources suggest that zig-zag lines indicate an experience of harsh reality and a need for comfort. Angular lines are also a feature of many styles of 'tag' graffiti and Manga cartooning, so may be preseny in the doodles of young people who are interested in these art forms.
Water-waves can be highly symbolic depending on the context, representing the water of life, a river, the ocean. The ocean is said to indicate an idle dreamer, though may of course be drawn by lovers of water sports. A curvy sine-wave pattern suggests musicality and natural rhythm. Wavy lines are sometimes drawn to represent long hair, meaning a desire for beauty and femininity (in ones self or a significant other).