Performance

Where the time actually goes.

Images first

Images are usually most of a page's weight. Correct dimensions, modern formats and lazy loading below the fold beat almost every other optimisation.

Set width and height so the layout does not jump as images load.
Defer non-critical scripts and load fonts with a fallback so text appears immediately.

Measure

Test on a mid-range phone with a throttled connection, not on your own machine. The browser's performance panel shows which request or script is holding everything up.