A good starting point for distance is the 40% rule. For example a straight 20 foot putt with 3 inches downhill I would figure it out about like this: (20 - 3) x 0.4 = 6.8 and then take the 6.8 away from 17 (20 - 3). That leaves me with 10.2 feet of power, I usually try to round that up a bit when I pull the meter back to make sure it rolls true.
This is not a hard and fast rule! Uphill putts will need a bit more, downhill will need a bit less, but it's a good starting point. Play with it, and develop a feel.
As for break....... well that's a little different. It's all about memory, feel and visualization for me. Some days I can't read anything, other days I can't read anything wrong... In this respect there is no substitution for experience.
Hope this helps!
Enjoy