Favorite recipe is to start with a sound concept. If you have that, all else falls into place nicely.
Technically speaking, I like a 250mm lens on 645 or 6x6, 135 on small format, or 360 on 4x5 for a tight shot. If doing a tight head shot on 8x10, I would really want an 800mm lens. A fast film is usually my film of choice, but if shooting small format, I will try to go as slow as the light will allow. I have used down to ISO 16 (Pan F), but usually I will use FP4.
For a not-so-tight shot, or a slightly environmental portrait, I like a 50mm to 85mm on small format, 150mm, 180mm, or 210mm on 4x5, 100mm to 150mm on medium format.
For an environmental portrait, anything from 90mm to 127mm on large format, 20-35mm on small format, and 45-65mm on medium format.
In short, pretty much every common lens imaginable. In the end, a successful portrait really comes down to what the picture is about, not the literal picture.