How to improve Google pagespeed insight score?

Please suggest me how to improve First Contentful Paint (FCP) and First Input Delay (FID) for my website ( on mobile. All the java scripts moved into footer, added async and defer on JS. Also, apply all the possible ways suggested buy the Google pagespeed insights tool but we did not see more improvement. We tried to defer and async all the CSS but while doing this our website gets break. Please help me to solve it.