Here you will need to decide on the type of pen you would like. There are bolt action pens, twist pens, cap pens, and click pens. Even with those options there are a couple of different varieties within those options.
Next you will need to decide on the finish of the hardware. There are a multiple finishes, however not all pens styles are available in every finish. For example there is gun metal, brass, aluminum, stainless steel, chrome, gold, silver, satin silver, pewter, antique finishes, and more.
Here you will need to decide on the type of body material. There are a lot of choices such as wood, acrylic, acrylester, poly acyrlic, alumilite, and metals. You can even combine/mix and match materials also. Exotic materials like, colored pencils in resin, pine cones in resin, and circuit board materials are all available (though at a cost).
Step 4 (optional):
On wood, laser engraving is available. Small images and text can be laser engraved on the wood, keeping in mind that there is not a lot of room on a pen body.