Like I said before, don't trade with anyone, just follow them on their quests so you get mad experience. Make sure you beat all the major bosses the first time by yourself, otherwise the hords will grab all the good items.
If you search the web, there are plenty of strategies to follow as far as using the skill trees wisely. If you don't have a plan, you won't get very far the second time through the game.
If you find decent items for other characters, create a new character and use it to store your items. Unless they changed it, if you start a passworded game and stay in for a few minutes, it will not disappear right away. Hide items outside of town and you can leave the game, connect as a different character and pick up the items. I do this whenever I find a good item and I don't want to drop anything I'm carrying.
