Lemon or Milk? It Depends on the Leaf
The rule of thumb for each, and the few teas that want neither. Most of it comes down to good water and a little patience.
Start with the water
A cup of tea is nearly all water, so whatever is in yours ends up in the cup. Filter it if the tap tastes of anything, and boil it only once.
Then give it time
Leaves need room and a few minutes to open. Taste as you go, and write down what you liked -- the next pot will be better for it.