From Before I Play
- Fighter+Thief and Ranger+Cleric are great multiclass combos.
- A Mage benefits greatly from starting as a Fighter. So pick stats appropriate for a Mage but start as a Fighter and dual-class to Mage after few levels. Be sure to pick a race that can actually dual-class though!
- Druids are awesome, especially if you have the Heart of Winter expansion (it added some spells). They get neat summons and AoE spells. I fought most of my battles by letting my Halfling Fighter+Thief scout the area, lure some monsters to the rest of the party and then have the Druid lay down some poison and slowing effects. You let your ranged characters take potshots at the trapped enemies and summon some elementals to help finish the job when the spells start to fade out.
- The expansion can be played during the main game or afterwards. I recommend the latter. It should automatically transport you to the new area when you finish the original campaign.