Team Build Help (newbie) (singleplayer)

I've been wanting to get back into the B&W copy I have, but I went to look at my previous team and.... it sucks lol. I would LOVE tips on how to build a good pokemon team in general (like what are some important pokemon, moves, strategies, archetypes, etc) and what kinds of pokemon I could build around.

Also, my favorite pokemon (and my team leader) is Throh, so if it's possible to incorporate it, I would enjoy that.

I would also like to be able to obtain a Darkrai for my team, but I'm not sure if it's possible anymore.