What the previous posts have said. Find two repeatable spots on your bike, head tube, bottom bracket, are the two I use, to take your measurements from. I make sure to parallel the seat tube with the ruler from the bottom bracket to the seat, to make the measurement consistent and repeatable. Also, though I realize this is more than obvious, find a level ground area to make your seat level measurement. Straighten the front wheel and get the bike as perpendicular to the ground as possible to set your seat level. If the seat is not dead flat, and few saddles are, start with what looks right and using a spirit level on two contact points, set it so the bubble is level. Then you will need to just ride the bike, there is no shortcut at this point. Also, set your front to back, knee over the peddle spindle, as a starting point and just work on the seat angle for now. Don't do two adjustments at the same time, move the seat forward a 1/4 inch and lower the nose. One adjustment at a time so you will know if that worked or made things worse. Hope this helps.
Frank.