How to go about improving website performance? [on hold]

I've been tasked to improve our website performance. I've never worked on such tasks before so i was seeking help from experts here who have worked on such tasks as to how to go about it? What will be the best tools to use for comparison? Any specific tools to use for minifying javascripts/ css etc? any tools that help us identify if any specific css or js is not used on the page etc?

Just a little guidance is all i am seeking.

TIA