the basic starting formation would be to use Nayeli as tank (on the right, towards the enemies), then put Bruenor in the second column. the spot below him will be where your main DPS comes from, and all other champions will be in place to apply buffs to that one. at first this may be Jarlaxle. you will want Calliope and Celeste to be behind him for their buffs. if you unlock Asharra, you can set her buff to elves and dwarves to make your DPS stronger.
if you find you cannot progress past a certain area, go back a little and kill enemies to earn gold (usually the areas just before bosses are the most efficient to farm). upgrade your DPS (you can hold left trigger to see who is doing the most damage), and purchase any buff upgrades that are affordable, and try again. using all your ultimate attacks at once, when all the enemies are stacked on your tank is a good way to clear a boss.
to complete the first tutorial adventure you only need to beat area 25, so it should not be very much trouble at all.