Just when you appear in town check your inventory and you'll notice that you have two kinds of potions (two potions of healing for warriors, one of healing and another of mana for rogues, and two mana potions for sorcerers) and a club. Sell the club, since it's useless and buy another potion of your choice.
Explore all the scenario/level you are, no matter what – that will help you get richer since you can have the luck of finding a rare, unique or magic item, which are profitable. Get and sell everything that you think may be lucrative, unless you plan to use it later. Use any armour you find in there until you get enough money to pay for something really good, or luckily find something great. You can make a lot of money from selling useless spellbooks as well.
Always pay attention to your mana and life pool, they are important. For warriors and rogues, learn only those useful spells (such as Town Portal) and use items that are for their class (melee weapons for warrior and long-range for rogues).
The game counts with several kinds of demons and monsters, and sometimes you'll notice that there will be some enemies that will appear with a golden text on it. That means it's an unique monster, or a "leader". Generally leaders come with an horde of same kind together with him. E.g., an unique Fallen One (like Snotspill) will come with an horde of Fallen Ones. And so on.
Unique enemies has a better chance of dropping better items. And it will give you more experience than normal enemies. Killing them is not a wate of time.
Some enemies may hold some strategy to get killed. Not an specific item or some kind of slayer, but tips to make you kill them easier. Something you need to know is that there are three kinds of monsters:
- Undeads: like squeletons, zombies and so on.
- Monsters: like scavengers, bats, etc.
- Demons: almost every enemy.
Memorize this: Holy Bolts have bonus on hitting undead creatures, and will only hit undead minions. On other kinds of minions, it will just pass through.
Some minions, specifically Diablo's minions, will only appear when close to you. They will keep lurking in the darkness till you get close enough to him attack you. Luckily, they are not quite strong, but that doesn't mean an horde can't surround you and kill you fastly. The way is to stay alert.
Another thing is that some unique foes and maybe even normals may hold some resistances, and sometimes immunities.
- Foes with resistance to some element (that can be fire, lightning or magic) or maybe all of them, means that the specific element will cause less damage than it should. But that doesn't mean he will not take damage, it just will get more difficult to kill him with that element.
- However, enemies with immunities means that the foe is completely immune to certain element(s). I.e., he will not take damage from that element spell.