All right then.
One of the basic things you have to learn about team building is team synergy. Team synergy is how well the Pokemon in the team can cover each other's weaknesses. An example is Ferrothorn + Jellicent. Both Pokemon resist each other's weaknesses (Ferrothorn resists Jellicent's Electric, Grass, Ghost and Dark weaknesses and Jellicent resists Ferrothorn's Fire and Fighting weaknesses).
Also, what tier are you playing in?