A lot of the answers are likely to lean towards "it depends." This focuses on your party lineup, spell choices and so on. If you focus primarily on damage dealing party members and know a fight is at hand, save prior, separate each party member using the chain feature and portrait drag, hide each member and set them up accordingly.
Once one character engages, use the character switch feature and attack with them, rinse and repeat.
If you are looking for more one shot tactics then use the Rogue sneak attack option.
If you are looking for something more exciting or explosive, use various barrels or have party members carry said barrels with them for such an occasion.
Learn to read the layout of the map/area and use that to your advantage. Electrify water, use the grease spell followed by a fire spell to ignite it.
Read your character spells. You can use sleep, charm, hold person, knock down/prone attacks to give you advantages over your opponents.
If you plan things accordingly, you will be able to easily win difficult encounters with planning.
If for some reason you are finding the area or mobs are to difficult, then I would suggest exploring elsewhere in order to level your party and then re-engage these mobs at a later date.
