What I see is that in general it looks like a good idea to underprice while building your stadium up. I won't give an optimum ratio because I think that someone needs to test it on their own and get a good "feel" rather than me giving some sort of hint.
when you underprice, it is hard to guess the attendance who is waiting i would make to high prices and check the free places and reduce the price to come closer to your arena size(make bigger steps if you build your arena after the last price update).