Bring a pan of unsalted water to boil. When boiling, pour in 2 tablespoons white (spirit) vinegar, and reduce heat to a
simmering water.
That is the
2nd important point: your water should not be salted (salt disturbs the cooking of egg white), and simmering, not boiling, because big bubbles boiling produce irregular and ugly poached eggs.
Prepare a bowl of cold water.