Too often than not the saddle on your bicycle is not fitted according to your height. It is true that some people like me for example prefer to have their saddle lowered down so that it is easier to use your feet for balancing when you are stopping. However this might have some bad implications on your knees in the long term and therefore is not good for every day commuting. So what is the correct saddle height based on your height and body type?
Basics: If you are standing next to your bike the height of the saddle should be around your hip bone level.
Technical: When you are sitting down on your saddle with foot on pedal, the angle of your thigh (top leg) in relation to your cnemis (bottom leg) should be within 25-35 degree radius. If you imagine it to be a clock face instead, and your thigh is the clock arm showing the minutes, it would be pointing at between 9 and 12 minutes. Or if it is hour, it would be somewhere around 2. My little sketch below does a much better explanation (please excuse my stick woman, obvs this is not in proportion to any typical cyclista).
Now who said that riding a bike is as easy as one, two, three (and you don’t need Maths and Biology GCSE?!).