Search for snow that is not ice to melt.
As Bruno said make sure to put some water in the bottom of the pan. Will save a minute or so of stove time. This is very critical if you have a teflon coated pan. Otherwise you will burn the teflon off the bottom of the pan and not only ruin the pan, but also ruin your batch of water.
Use an aluminum pan. They are far better than stainless or Titanium for conducting heat, but must have a wind screen otherwise the aluminum pan will conduct its heat to the outside very quickly.
When melting you do not have to keep it on the stove till ALL snow chunks are out, just most.
Stir the snow water mixture. In otherwords BREAK up the snow/ice chunks!
Wind screening is CRITICAL. Without it you can sometimes forget melting water at all.
Whatever stove it is, put on as high as possible.
Always carry a thick aluminum foil to put around the pot so the wind can't hit the pot.
Make sure to always put a lid on the pot. Hopefully a lid that is larger than the pot itself as it will cup the heat coming up the sides of the pot.
Dig a hole in front of your tent or in your vestibule and boil the water there as it will cut down the wind to very little.
Melt the water inside your tent proper, but it requires a larger tent, or suspending your stove from the ceiling which has other problems.
Put the Stove on an aluminum shovel. It will reflect heat. Otherwise your stove will melt itself right into the snow and put itself out. Or you have to carry a base plate which is just extra weight with no function.
and... Relax its going to be a while...
Oh, and make sure you have a good and properly set up windscreen & ground reflector.
A quality pan makes a difference as well probably. And a lid to put on it