What's the best way to level my warrior?

As a Warrior you usually fall in to one of two roles, you're either a tank or damage dealer. Since you're wielding two-handed, you should probably be aiming for the damage dealer role (a tank, ideally, would be using a weapon/shield combo for its defensive properties).

As such, for a damage-dealing Warrior, your attributes should be considered as such:

Strenght is your primary attribute. It increases your damage output and attack rating, it also increases your fortitude score (which makes you harder to knock down, stun, etc). It is a required stat on most Warrior gear. You should maximise this as much as you can.

Constitution is your secondary attribute. It increases your health and is a required stat on most Warrior armour. You should ensure it is at least high enough for you to wear the best armour you can currently get your hands on (but probably not much higher).

Willpower is also quite important, it increases the quantity of stamina you have available for your abilities. If you keep running out of stamina, pump a few points in to this.

Dexterity and Cunning are less important, and can be neglected. They increase the frequency and additional damage of critical attacks, but you have abilities that can do the same more effectively (eg, Sunder, which also staggers enemies on criticals). Cunning also increases your defense rating.

For a Warrior, Magic only adds a small % of magical resistance - the points are better spent elsewhere.

In terms of abilities, you should probably concentrate on the Two Weapon and Vanguard trees - both of these will help maximise your damage output - and also maybe the Battlemaster tree if you need help maintaining your stamina.

And you probably want to look at the Beserker and Reaver specialisations.

Finally, remember that a damage dealing warrior is not a Tank, they can and will fall if unsupported when under sustained or heavy attack.

If you read the attribute descriptions they will give you a good hint on what to focus on.

Strength for example gives warriors more damage, willpower more stamina to do actions with, etc.

As a physical damage dealer you can pretty much ignore magic. There are other considerations to make as well. If you're low on health and notice you are dying a lot, Constitution will raise your health.