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).
Enemies
Some enemies may require a specific strategy to be killed. Not a 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 other enemy.
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 until you get close enough for him to attack you. Luckily, they are not quite strong, but that doesn't mean an horde can't surround you and kill you quickly. The way is to stay alert.
Resistance and immunity
Some unique foes and maybe even normal ones may hold some resistances, and sometimes immunities.
Foes with resistance to some element (that can be fire, lightning, 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). Meaning, he will not take damage from that element spell.
Unique enemies
The game contains several kinds of demons and monsters, and sometimes you'll notice that there will be some enemies with their names in gold. That means it's a unique monster, or a "Leader." Generally, Leaders come with a horde of the same kind of enemies. For example, a unique Fallen One, like Snotspill, will come with a horde of Fallen Ones.
Unique enemies have a better chance of dropping better items, and will give you more experience than normal enemies. It is definitely not a waste of time killing unique enemies!
Quests
Throughout the exploration of dungeons you may come across some quests, but not others. Unique to Diablo is a level of randomness that actually excludes some quests from gameplay. This means that during a game, some quests may not be available at all. This feature emphasizes re-playability.