Line is one of the most important elements of design you should be thinking about when drawing. In every drawing you make, any marking, no matter how big or small is a connection of dots, which is a line.
Line is used to show movement, define shapes, determine the size of shapes, suggest a certain mood or feeling and give direction.
Every mark you put on your page is made up of many of them. Although you can not see them all with the naked eye, if you would examine your mark under a microscope you would see that hundreds of them that make up every dot on the page.
To illustrate this, you could take your graphite pencil start drawing dots all over the page that connect to each other. Eventually you will end up with lines all over your page.
When you are drawing, your lines convey a certain mood or feeling. If you want to create a scene that is peaceful, calm, or happy you would use a lot of curved lines because curved lines give a calming feel to your drawing. These lines are usually light and flowing. If you are drawing a scene of and would like to convey unrest, you would use jagged angry lines. If you are angry and you want to scratch out a mistake you made, I highly doubt that you would use nice curvy lines. Instead, you will use multiple jagged ones. The darker or bolder they are, usually means the angrier you are.
Bold lines - strength, power, stability, and might
Branched lines - unity, strength and focus.
Circular lines - busy and active
Curved lines - happiness, harmony, peace, and tranquility
Dark, slashing lines - aggression, anger, and rage
Dark, heavy lines - confidence and boldness
Diagonal lines - rhythm, movement, and harmony
Fuzzy lines - soft, gentle, and relaxed
Vertical lines - stability, strength, and power
Line is the simplest way we can convey to others our mood or feelings. What mood you are in and type of person you are is often reflected in how you draw, which is why people draw in so many different ways.
So, the next time you choose something to draw, think about what types of lines you want to use. What idea, mood, and feeling is going to be reflecting in your work.