Here is my 2 cents.
You must understand that you cannot do a wax up adequately outside of the arch. This may seem stupid, but I have seen many a new dental student slave away on a wax up until it looks great... only when they put it in the arch it is all wrong.
I like the subtractive method myself. Build that sucker up to about 125% of what it should be and start shaping it back. Begin with the proper incisal/cusp tip placement (i.e. it should be in a line with the other teeth. Next carve out your embrasure spaces. If you do not know what these are, ask someone or look it up. Basically, they are the angles formed by the meeting of teeth. If I could, I would draw you a picture here, but I cant. Check the opposite teeth for an idea. There are LOTS of embrasure spaces to carve out. Once you get this concept in dental anatomy, then you will understand why Angle Ranking is the most relevant portion of the entire DAT.
Then move on to emergence profile, or at what angle the tooth comes out of the gingiva. Again, the other teeth in the arch will show you the correct angle. Then you need to dial in your occlusal anatomy. I cannot tell you how important it is to be able to do this well and to do it quickly. When you do your first occlusal fillings, then you will understand why you are forced to do this in a timed fashion, especially when the setting time of your material is around 5 minutes.
To do occlusal anatomy, first define your central groove. Then rough out your ridges. Again, consult the opposite tooth and the adjacent teeth to give you an idea for position of both the central groove and the ridges. I know this might seem a little premature, but if you develop a sequence and stick with it, then you will be working on an very relevant clinical skill. If you don't understand how to re-create occlusal anatomy then you will be forever adjusting your fillings and that sucks for you and your patient.
Once you have your wax up pretty much roughed out, then it is time to sexy it up. That has been explained pretty well elsewhere, so I wont go into that.
Let me just sum this up: wax ups are, in my opinion, training for restorative dentistry. Learn to get clues from adjacent teeth, learn to see and compare angles from those teeth. Try and work quickly. I would also recommend sticking with a carving instrument that you would find in an operative tray, such as a Tanner Carver or a Half Hollenbeck, because your wax carving skills will merge into your amalgam carving/composite shaping skills.
A little bit has been said so far about the additive method and the subtractive method. Both are ok, in my opinion for these reasons: amalgam carving will be mainly subtractive and composite will be additive. But for beginners, the subtractive method is the easiest. You dont want to spend an hour and a half adding wax slowly, only to realize that you added too much here and too little there. Just add too much and then you know where you are.
Good luck.
