I do a new black with 2.5 gr leaf to 6 oz boiling water in a preheated mug and infuse for 3 minutes. Subsequent infusions typically run something like 4 m, 6 m, 8 m, 10 m. I expect at least 3 good infusions from a good quality black -- whether China, Assam, Ceylon, Himalayan, Nilgiri, or Darjeeling. It it can't deliver a minimum of three infusions I wouldn't consider re-ordering. I am happier with five infusions, and most good blacks deliver that for me at least occasionally. Often, once I get to know a tea, I use more than 2.5 gr of leaf and almost always use more for the China blacks.
For gong fu blacks I will do something like: 3.5 grams in a 100 ml gaiwan, just off boil, infusions: 1 m, 90 s, 3 m, 5 m, 10 m, plus a couple long, untimed infusions. I think you might get better results with still more tea and shorter infusions, but I haven't played around too much lately.
For astringent, rough Assam, I like to make it in a large yixing pot a little stronger than my standard Western style. I find that the yixing helps take the nasty edge off. Proinsias taught me this trick.
Needless to say, I never use milk or sugar.