If you steep grains first for half hour or so at 150°F, turn the flame off at that point and add all of the malt. Stir until dissolved. Put the heat back on and bring to a boil stirring all the while. Add your bittering hops once boiling begin the timed boil. If you don't steep grains (and really you should for a better beer) just warm up plain water to 150°F or so. That's enough to help melt and dissolve the LME. After that, switch to DME which keep better and use it in the same way (just use about 80% as much by weight).