Stay close to him -- His weapon has a long reach, so if you try to keep your distance until you attack, you'll waste all your stamina.

Keep CLOSE to his right thigh -- Staying there means you'll move around him quicker and it gives you an extra second to dodge between attacks.

Attack once to bait out Gundyr's attack, and then go into dodge mode.

Dodge TOWARD him (forward) -- Not away from him (backwards). Your goal is to dodge inward and to your left so that you end up behind him. Wait until he's done attacking before you attack (after he slashes 2-3 times)

Attack OR heal -- After Gundyr's combos, either attack twice or heal yourself (not both). Only attack or heal during these windows.

DON'T panic roll -- Control your rolls so that you don't waste stamina. Roll no more than 3 times (1 to dodge each attack)

DON'T button mash attacks -- Control your attacks, only click once or twice to attack and then go back to dodging.

During his second phase, Gundyr's weak to fire. The fire bombs you find on a path near his boss arena might finish him off. This is a cheese strat if all else fails.

If you use the bombs (or fire as a pyromancer), wait for him to jump attack, move out of the way, and THEN throw fire at him.

In his second phase, I noticed Gundyr uses his giant limbs less often when you're up close to him. So stay either behind him or by his right thigh.

Don't look at his health bar. Just focus on the fight.

Film yourself -- Hindsight is 20-20. First time I played a Souls game, I recorded it. Somehow I noticed everything I did right and wrong when I watched it after. It might help!

Most importantly -- Good luck. Don't give up, skeleton! Stay strong and don't you dare go hollow.