It may have been mentioned earlier, but keep in mind the volume of water you may need to use to wash any extract from the cans or bags that they come in, not to mention the displacement of volume for the LME itself. If you start with a full 5-6 gallon boil, w/o being careful you could end up with way too much than what you need by the time you sparge your steeping grains and add in the LME.
I don't know if it's the best way or not - as I'm still pretty new myself, but the few that I've done, I've steeped in 4 gallons or so and boiled till it's time to add the extract, then I'm able to flush the containers out and top off as needed w/o worrying about adding too much volume just to have to boil off later.
Admitting, I've only done 3 full boils so far, but they seem to have went well using that process.