you'll need a clean area to work, keep the coloured plastercine apart (you dont want the colours mixing. ALWAYS have clean hands, keep a packet of wet wipes at your side, you'll use loads
have a picture/pictures of the model that you are making, take your time and start with the head, dont move on untill you get the head just how you want it, this alone can take you many hours so you'll need lots of patients
if its your first model, try making a morph as he is only 6 inches and wont need an armature (wire frame inside the model) hope this will of helped, good luck