There are a huge variety of teams that all have different tactics in Blood Bowl. However, it usually comes down to three general categories: Beaty Teams, Balanced Teams, and Finesse Teams.
Beaty Teams (Chaos, Lizardmen, etc.) Have high armor values and strength on their main linemen. They tend not to have many skills standard. Their journeymen have a gimmick that makes the team more than a bunch of walking beat sticks. For example, Chaos Beastmen have Horns, making them great on a Blitz. Beaty Teams need to hit the enemy hard and team up to get two or three die blocks. Keep pressure on until you break armor. Open up avenues for journeymen to score touchdowns.
Balanced teams tend to have average stats an armor, backed up with one major skill per player, such as the human lineman who has Block. Balanced teams need to work together to set up passes and protect the ball carrier. Occasionally they can team up and hit an enemy hard, but they usually can't go toe-to-toe with a Beaty team.
Finesse teams have great Agility but low Armor and Strength. They also tend to have specialists that fulfill roles. Finesse teams need to end up at least one square away from the enemy so that they can only hit one of them a turn. They also excel at running and passing, so they need to score points. Don't underestimate them; they can move fast and team up to smash an unwary opponent.
Essentially, each team has to play to its strengths. My Konquata Monitors need to go to the pitch and beat up the enemy, while they make avenues for the skinks to run the ball. They are fast for a beaty team, but lack of skills makes me rely on re-rolls to do anything more complex than smacking the enemy.