Experience

Experience is the basis on getting your lvl ups which results in +1 skillpoint and +5 statpoints each.

Also every lvl adds base life, mana and stamina. The amounts differ between the chars, check out Char specifics for more information.

How to get experience:

You get experience by killing monsters.
There is an experience shrine which grants you +50% experience for 144 seconds. Try to use them as efficiently as possible.
Quest rewards do not give experience.

Basic white monster

They are the basis for any other type of monster.

They are easy to kill but very bad for experience compared to the following monster types.

Champions

2-4 monsters each group - Avoid them when there are only 2.
+300% Experience
+2 monster lvl
Ghostly champions have "spectral hit" - they do elemental damage every hit. This can be very annoying on ranged monsters.
Shamans from act 1 and 3 are the monsters you want to be champions, they give very good experience.

Bossgroups

Boss and minions +500% Experience
Boss and minions +3 monster lvl
A random ability out of the list you can see here: Link
They are your main experience source.

The goal in every speedrun through norm is to get lvl 20 in the 'Chaos sanctuary' (act 4).

The reason behind this?

You have to be lvl 20 to get the ancients quest in act 5. This is a requirement to finish the game, because you can't go on without this quest.

Lets see how we get there most efficiently:

Until 'Andariel' - You want to focus on bossgroups here. Only kill basic monsters if you get a large group of them. Depending on the character you want to reach between 13-14.5.

'Blood Moor' - you want to get lvl 2 here. Zombies are the best experience in this area.
Act 2 - 'Far Oasis' and the 'Rocky Waste' with beetles are awesome expierence. But you will have to kill other nomal monsters aswell - just try to get little groups of monsters. lvl 17 should be your minimum goal for 'Duriel'. The Sorceress is the exception. You want to be 18 with her.
Act 3 - The 'Flayer Jungle' is the area you want to clear for experience here to get close to 20 before 'Mephisto'. Amazon and Necro should be lvl 20 before 'Mephisto'.