There's only two factors that matter when poaching eggs - egg freshness and water temperature.
If your eggs aren't fresh you're fighting an uphill battle but the workaround is to crack your eggs into a fine mesh sieve or tea strainer first. If the egg is fresh, barely any will pass through the sieve, whereas if it is less fresh some of the white will pass through. If you had put the less fresh egg into the water, those bits of white that pass through the sieve would separate from the main egg and make a mess everywhere.
The water should be as hot as you can get it before any bubbles start forming.
Vinegar is NOT necessary. Don't listen to vinegar shills.
Swirling the water to create a vortex is OPTIONAL. Swirling will create a more aesthetic egg, but won't affect overall quality.
Other than that it's fairly simple. Crack the egg into a cup or ramekin first so you can gently plop it into the water. I think about a 3 minute cooking time is right but ymmv.
The cling film method also works... if you're a huge pussy!
