Fix my core web vitals and site speed

I need someone who can fix the site speed and core web vitals of my site. Someone did it before and didn't tell me the steps so I could maintain. This is why I need it doing again and I need someone to tell me all the steps so I can maintain them. I'd also like to add that some optimisation plugins collide with my theme so we need to use things that don't. I was previously using a plugin that made random images on my site disappear.