Ale, I'm pretty new at wine making also, everyone else is probably at work, so I'll tell you how I do it. Let wine go dry, SpGr below 1.000, check it for three days and if it doesn't go any lower - it's dry, which means that the yeast has done all it's going to do and all the sugar has been converted to alcohol. Then stabalize with Sorbate and K-Meta, let this set for at least 24 hours, a couple of days would be better, this to make sure you have no further fermentaltion due to adding more sugar. Then after you are sure it isn't going to ferment any more, you can add you sugar. Make up a sugar syrup using 2 parts sugar to 1 part water and heat this up, not to a boil but pretty hot so the sugar will disolve in the water. I used to use my must for this, but I recently read a article that said not to use the must but use water, something about lowering the alcohol content. When all the sugar is disolved the syrup will be clear, let this cool before adding. Use the "wine cal" found in the top section of the home page to get a idea of how much sugar to use to get to the desired SpGr, don't add it all at once, slip up on the desired SpGr. Add a little and take a SpGr reading, this will give you a idea on how much more you need, after adding the sugar stir good before taking the SpGr. I have a sweet tooth and backsweeten mine to 1.020 to 1.025. After backsweetening I like to de-gass again. Hope this helps until someone with more experience answers you question.
Semper Fi