A Personal Favorite
Graphite is by far my favorite art medium to practice with. Why? For one, holding a pencil is a natural thing for everyone, so starting out with graphite isn't so scary. More importantly, the fine tip of a pencil allows you to achieve greater detail than any other art medium.
Graphite is typically sold in sets of pencils with each pencil having a different number. The number represents how harsh the lead is. The harsher the lead, the darker and thicker it will show up on your paper. Certain lead types are also more difficult to erase than others. Although some artists like utilizing a variety of graphite pencils in their pieces, one can probably achieve the same effect with just one pencil and by adjusting the pressure applied to the paper. One can also use a regular pencil from an office supply store and achieve similar results.
Graphite and pencils are pretty forgiving in that they work on a variety of surfaces. Art supply stores sell sketch pads made specifically for graphite users. Regular smooth paper can also be used or even thicker, vellum paper. This is up to the artist and his or her preference.
One technique I enjoy using with graphite is mixing medias. Once you are comfortable using different art media, you can combine them together in one piece to create something totally unique. When utilizing mixed media, make sure you are working on a surface that supports the various media you are working with. For this piece, I used a simple wet media paper that came in an art pad. The medias I used were graphite, acrylic paint with water and ink. Feel free to experiment with different medias and see what looks good together. As the artist, you have the ability to create and experiment.
Tips and Tricks
One trick I use in almost all of my graphite pieces, which can be used in any art medium, is gridding. Gridding allows for a proportional piece. It can sometimes be a tedious task, but always creates for a more life-like final product. Here is a simple video on how to grid your paper before beginning to sketch.
Here are some photos I took as I was working on a sketch. As you can see, after I draw my figure, I erase the gridlines so that they do not show. For this reason, if you are using the gridding technique, make sure to draw your gridlines as softly as possible so that they will be easy to erase.