The correct way to brew black tea: one spoon per cup and one for the pot, water at a rolling boil, steep four minutes, and stop apologising to the leaves. My grandmother used two teabags and called it 'war tea'. I have never recovered. The tea must be strong enough to walk out of the cup on its own. Salt, if you are a certain kind of grandmother, and mine was. The pot must be warmed. If you are not warming the pot, you are making soup.
Milk in after the water, and if the cup is cold you can absolutely warm it first. I will die on this hill and the hill has a kettle on it. Also, if you are making tea for someone else, make it the way they like it, not the way you like it — that is the whole of hospitality. The cup-warming thing is not optional and I will hear no more about it.
The correct way is the way the person drinking it likes. That said: milk on the side, pot warmed, and nobody is allowed to say 'tea bag' in front of the kettle again. Locking my own rule in before someone quotes me on it. This thread has become the longest-running civil tea debate on the board, which is either a good sign for the site or a very bad sign for us.