Conceptualize the look you want for your 3D image. You can do this by hand or digitally-drawing a still image. Collect all 3D modeling data required to design your image in the computer. The data may include those acquired from a motion-capture camera or those acquired from a 3D-scanned scale model, especially for 3D images meant to be used for animation productions. If you are only designing the 3D image and not animating it, use your still image as your primary guide for your design.
Start making your 3D model using a 3D-modeling program or an animation program that is also capable of creating 3D models. This model serves as the skeletal system of your image, which is essential in finalizing its look. The 3D-modeling process requires the creation of "avars" or hinges, which are dots that compose the 3D image's skeletal system. These dots -- forming various geometric entities such as lines, triangles, rectangles and flat and curved surfaces -- are required to complete the image's shape. Collectively, the avars you make also work as bones and joints, which are important when intending to use the 3D image for an animation project.
Form and shape the body, skin and/or surface of your 3D model. Incorporate all other body or object parts to cover the 3D model's skeletal system. If your design is a human character, design the clothes and establish the character's personality based on its physical attributes. If your design is an animal or object, design its physical attributes accordingly as well.
Render your final 3D image and export it to your desired file format.