80% of Bruno's Pokemon are of the fighting type and a rock/ground type. Very easy, it seems. Far from it. Watch out for that Hitmontop.

Psychic moves on Hitmontop, Hitmonchan, Hitmonlee, and Machamp. Water or Leaf moves on Onix.

Karen uses Pokemon that are of the Dark type, look like Dark types, or half Dark types. She is rather hard but can be easy when you know her weaknessess.

For Umbreon, use Fighting moves.
For Murkrow, use Electric moves.
For Gengar and Vileplume, use Psychic or Fire moves.
For Houndoom, use Water or Ground moves.

I know what you're thinking: crap! Don't worry, Lance is rather easy even with all those Dragonites. This is why you will need alot of Full Restores.

Ice moves on his Dragonites.
Water, Eletric, or Rock moves on Aerodactyl, Charizard, and Gyarados.