Whether you are starting a project first thing you need to do is come up with a concept. A concept is a blueprint or guide for you to follow. Take some time to find reference for your project. If you are sculpting a character from comics or another source get as many angles as you can, include front back and each side. Take note of any equipment the character carries, if it is something from real life gather as much reference for it as possible. If it is a specific item created for the character again gather as much reference as you can find. The internet is a resource library you can draw from to find reference. Another great source for reference is your local library.
Once you gather all your reference you need to organize it and condense it into “cheat” sheets that you can refer to easily and display in front of you. I often use Photoshop to create reference sheets for each specific part.
At this point you need to take some time to consider each aspect of your project and jot down any notes you come up with on a rough sketch such as pose and height. If you are doing a conversion plan how you are going to alter it's pose. Record any alterations on the rough sketch. Plan out the details you want to add or alter and record it on your sketch. Plan out any other details like weapon, head or hand swaps. The rough sketch will give you direction throughout your project and help you anticipate any problems you may encounter.