Upgrading your weapon has more impact than upgrading Strength or Dexterity in terms of increasing damage. So in the early game, if you have a limited number of souls to spend and you're wondering if you should spend them on Titanite shards or on a level up, probably go with titanite shards if you're worried about being able to hit harder. Of course you'll still want to focus on Strength or Dexterity(or both) *some* because you'll need them to be high enough to use certain weapons. So find a weapon you're comfortable using and upgrade it ASAP.
Dont ignore the Adaptability stat. You can of course hunker behind a shield for much of the game, but generally, rolling to dodge is a more efficient way of avoiding damage. Somebody hits you with your shield up and it takes a nice chunk of your stamina away, if not damages you outright because you didn't have much stamina. So improving your Adaptability stat gets you improved rolling, with bigger windows of invincibility to roll through attacks. Highly useful for many boss battles as well.
As I allude to above, watch your stamina carefully. Stamina management is very important. You've probably encountered this some as a magic caster, but it's even more important as a melee fighter because you need to balance attacking and defending at the same time on the front line.
Most people prefer to keep their equip weight fairly low(<50%), to get faster and farther rolls. Each 10% will have an effect on your rolling and your stamina recovery speed. You can of course choose to go with heavy armor and a very slow and less usable roll, but I find even heavy armor doesn't mitigate damage enough to make it worth it. Better to work on avoiding getting hit than to just rely on tanking in my opinion.
Learning to parry is useful, but optional.
Dark Souls 2, unlike Dark Souls 1, tends to favor Strength scaling over Dexterity scaling on weapons. So while you can still do just fine with faster Dexterity weapons(or things like spears), the best damage output builds tend to be Strength-based. Use what you're comfortable with, though. Obviously bigger weapons weigh more, use more stamina and are slower to use, but if you can adjust, they are very powerful.
Buy a bow or crossbow and ensure you're regularly stocked with arrows or bolts. There will be times where you will probably want to cheese an enemy from a distance rather than tackle it face-first. Alternatively, you can invest in a bit of magic for a hybrid build. I dont have much experience with that, but I know a lot of people like to do that.
Most importantly though, you're just going to have to really learn enemy attack patterns now. Learn when to roll or when to block. Learn when to strike. Learn how to position yourself for highly useful backstabs(cant do this on most bigger enemies, just to warn you).
