Make sure that you finish the trophy quests before leaving each area. You cannot go back to do these later, and you will miss out on an end-game weapon if you do not do them all.
The only place where you can really hurt yourself in terms of character development is wasting skill points, so take a careful look at the descriptions and think about how you want to play. The easiest route is probably Fire+Melee, ignoring all other spell upgrades, though there are a number of ways to play. The skill for advanced techniques in hand to hand will help you get through the boxing minigames, but the charge-up boxing power is not very useful. Likewise, the power to reduce drunkenness time is not useful -- you can always use a potion if you need to.
You can get a 3-red meteorite sword by the end of chapter 2, if you are careful, and it will last you a long time.
Don't neglect potions and sword oils. Having a sufficient supply of these will get you through most encounters. Make sure you also keep at least a small supply of the one that removes toxicity -- you will not always have a campfire on hand to rest it out.