Moka pots are temperamental. It took me a while to figure out quite how to use mine. Makes great coffee once you're used to it, though.
You probably want to pre-boil the water so that the coffee doesn't sit on the heat for too long, but you should also only turn the stove up to medium so that it extracts more slowly. Pull the pot off the heat as soon as it starts making the loud rushing noise — I even rinse the base with cold water so that it stops boiling right away.
It was the sieve and the seals that always got me. And my tendency when presented with a hot cup of coffee to actually drink the coffee instead of cleaning the equipment.
I've tried it all, and the only thing that I'm happy with is the Aeropress. If that isn't the perfect cup of coffee, I don't know what is.