The two best options..If it's really cold, are A. Ice Armor gloves or mittens with chemical handwarmers..They have a pocket for the warmers on the back of you hands which heat the blood supply to your fingers. B. Gerbing Core Heat gloves with rechargeable Li ion batteries and heating elements all the way to your fingertips..The best I have found after trying everything else mentioned here.
Failing these options, try the small pair of chemical warmers and tuck them into your gloves on the back of your hands. Keep a pair going in your pockets for when you need a quick warmup and your hands need to be bare (Hot Hands seems to be the longest lasting brand)..I have used all the above solutions in -20 to-40 deg. F while using view cameras... Evan Clarke