3. Photos! Photos! Photos!
Try to absorb as many reference photos as you can of your chosen subject from as many angles as possible. The more information you have about their features, the more accurate your representation will be. As a bare minimum ensure you have at least one front view image and one profile image. If available, use multiple monitors so that you can compare the images with your 3d model simultaneously.
If you are already familiar with 3D modelling in applications such as blender, this open approach may make you feel uncomfortable as you probably like to import a source image into your application and use that as a map to create vertices. However extremely accurate results can be achieved using the techniques described in this tutorial. Using the morph dials in Daz Studio is more akin to sculpting and this greater freedom allows for some excellent results.
If you have chosen a very popular celebrity, there may be a large number of images available to choose from. An important tip to remember is to try to select reference photos from the same time period. Celebrities often undergo cosmetic procedures, even though they may vehemently deny this in interviews! This factor along with natural ageing can make your task difficult if you’re looking at photos taken from different years.