What are the best stats to focus on for a warrior?

Your starting class just determines the equipment and stats you start with, and so you are able to grow the character in any direction you wish. The most important thing to keep in mind when building your character is the following (source):

When it comes to developing your character, there is one thing you should keep in mind: You should only boost one offensive stat. This includes: Strength, Dexterity, Intelligence and Faith. The reason for this is that most weapons have stat scaling. So if you have a weapon which scales with strength, and you decided to split your points between dexterity and strength, all of the points invested in dexterity are essentially useless. That isn't to say you shouldn't put any points into the other offensive stats, just that you should only be putting enough to meet stat requirements for equipment.

If you've started as a Warrior then your best bet would be to focus on either a Strength or Dexterity build. This just boils to personal preference, since both are effective.

Dexterity based builds tend to focus more on mobility. The weapons available to Dex builds tend to be faster than those from a strength build, and Dex based characters can make effective use of bows (most bows scale good with Dex). However, most of the good shields have high Strength requirements so Dex characters will need to rely more on dodging to avoid being killed. The increased reliance on dodging also means you'll need to ensure your armour is light enough to not impair your movement.

Strength based builds tend to be more tanky. The weapons available to a strength build are usually slower compared to those used by dex builds, and strength based characters are able to make use of shields to block damage. Being able to wield a shield makes dodging less important, which also means you'll be able to wear heavier armour since decreased movement isn't as large of a concern. Strength based characters are unable to make effective use of bows though. If you do decide to make a strength based build I'd suggest looking at this answer where I go into more details on tank builds.

Some additional details (source):

The key difference between Strength and Dexterity is the type of weapons you use. Strength favours weapons like Axes, long swords, and great swords; where as Dexterity favours spears, katanas, and curved swords.

Of the two stats, I personally suggest using Dexterity over Strength because (source):

Although all bows scale with strength, it is very low, whereas all bows have very high scaling with dexterity. Due to this you can easily dispatch enemies from a distance with your bow. I cannot emphasis how helpful this will be throughout the game. Not only does it let you dispatch enemies before they get to you, but also allows you to dispose of archers as soon as you see them, instead of being forced to dodge their arrows as you fight your way to them. Due to this, I highly recommended a dexterity build over a strength build.

Other stats you'll want to focus on are Vitality and Endurance.

Vitality increases your health, but after your invest 40 points into Vitality you start to suffering fairly severe diminishing returns, so I'd stop investing points once it hits 40.

Endurance increases your Stamina and Equip Load. Higher Stamina means you can dodge, attack, and block more often. Equip Load means you can wear heavier equipment before suffering from impaired movement. I wrote this on Endurance about tank build, and it applies equally well for Dex builds (source):

Similar to vitality, endurance becomes less useful after 40 points since stamina will stop increasing, and only your equip load will increase. I would suggest investing no more than 40 points into it because of this, but you will probably be able to get by only investing around 30 points.

Another stat you may want to invest points into is Faith, but only enough so you can make use of the Heal miracle (12 points). It'll give you a little bit of extra healing, which can be really helpful.

The thing about Dark Souls is that the starting class does not matter aside from the initial alloted stat points and the gear you pick up in the "tutorial".

To answer your question "What stats do I need to survive more easily?" I would suggest Endurance, Vitality and Strength. This way you can (and should) equip a weapon that would normally need two hands in one hand and then have a shield in the other (thanks to the strength). On top of this you will be able to equip the heavy armours without too much of a penalty on your movement (thanks to endurance). Vitality speaks for itself, I'll leave the rest up to you since the best thing about Dark Souls is finding your own way through the madness.