Idiom for "the first attempt (of something) is never right"
In Russian there's a saying that 'the first crepe always comes out wrong' (literally 'stuck together into a ball'), meaning that you'll have to try more than once to succeed at something - because crepe batter is usually trial-and-error.
What's the appropriate English translation?
From software engineering: Build one to throw away.
It may not be the exact translation, but
Rome wasn't built in a day
may convey the same meaning here, depending on your usage.