USING LASS AGGRESSIVELY
This is pretty much how everyone uses Lass.  You empty your hand of Trainers,
then empty theirs.  :p  The best time to use this is on the first turn,
because their hand will have a few useful Trainers in it, and unless they
draw an Oak, there isn't anything they can do to retaliate.  Another good
time to use it is when you're wearing them down and they're waiting for just
the right moment to use their Trainer.  If the Alakazam is transferring
damage to a Chansey, wait until they're about to PokeCenter/Scoop Up, then
Lass their… (hmm… what rhymes with Lass…? hmm…)

USING LASS DEFENSIVELY
Unlike the other method of Lassing, this technique is normally used later in
the game, when you're coming close to getting decked.  Say you're playing a
Raindance.  You've already got a Blastoise out, so there's a useless Breeder
sitting in your hand.  Just use Lass, and you've gotten yourself an extra
turn!  Plus, you've thoroughly disrupted your opponent!  If there's more than
one Trainer in your hand when you Lass, you've gotten yourself that many more
turns.  Also, Lass presents another opportunity to beat Mulli-Mewtwo decks. 
One Lass, and it's over (as long as you don't Oak or anything).  You have
more cards in your deck than they do, and there's nothing they can do about
it.

MORE LITTLE COMMENTS
* Lass works best in decks like InSaNiTy.  You can use it to disrupt, or to
prevent decking.
* Be careful when you Lass.  You can't just Lass whenever you want, like
Bill.  You have to time it just right, and Lass when the moment is right. 
Timing is everything.
* Remember when everyone thought this was the worst card ever?  Now people
love it!

Hitmonlee