If you already know which spells are good, simply pick them early in your new game.
Tactician is relatively more difficult in the beginning than in the end, likewise normal mode, but the learning curve is ok if you already completed the game in normal.
In general, fights are made easy by having initiative (a few leadership points and speed?) and controlling ennemies asap (mage spells, man-at-arms knockdowns and marksman special arrows).
You might want to pick different companions so you discover their stories (what did you do the first time?).
The very first fight can be difficult if you don't select proper skills. The spider summon, the heal, the frozen cc, ricochet and knockdowns are very good to take at creation for that fight. Scoundrel invisibility is handy to ransom the city right after.
It might be helpful if you gave your current thoughts on what you'd like to build and why, as it would be easier to simply react to it rather than write a full guide.
I took 2x mage, a 2h melee and a ranger. I'd have one mage focus on Fire/Aero (but also some points in other schools for novice spells) and the other focus more on Geo/Hydro/Witch as a buffer/CC'er. I'd usually buff my ranger/melee to deal high amounts of damage.. and I'd only use one mage to heal, since melee also has a heal. Melee also would use Encourage a lot, since I like it.. don't know if it's all that effective, but I like the idea. So I usually take Madora and Bairtor (or whatever her name is xD). I read some guides and this guy claiming he played over 500h is talking about dual wielding mages pumping points in strength AND int.. dex AND int (ranger variant) focussing ALL magic schools. Sounded a bit too much jack-of-all-trades to me.. So I came here. Hope this help(?) If not, ask me what you want to know exactly : )
