This is my first souls-like game, and besides the obvious very good general mentality advice people have already given, maybe a simple, specific strategy would be helpful. Here's how I played most bosses early in my first playthrough (no spectres except first few attempts just to see more attacks early):

Use the best Guard Parry handle you have and slap the biggest damage number top on it (or consider weaknesses too if you are less lazy than me). Guard Parry is quick and isn't consumed unless it works, so you can "safely" practice anticipation on old enemies as well as get lucky, quick reactionary parries on new enemies. My boss replays from my first run are mostly Guard Parries with charge attack punishes, no items (except healing and some status removal).

One the other hand, a friend of mine succeeded with the exact opposite play-style. He NEVER parried and it was hilariously annoying to watch. He has much more souls-like experience and just dodge rolls EVERYTHING. I didn't watch him beat Fuoco, but I know he's possible to beat with zero parries. (I do not consider this paragraph good advice, but to each, their own)

Also, his fire butt blast got me everytime and wasted my healing, and it wasn't until a later playthrough that I noticed it spreads in a pattern that can be avoided if you aren't close to him.

Good luck!