Opening paragraph. Start with the situation the reader is in, not with a definition.
Spacing
Most pages don't look amateur because of the font. They look amateur because everything is the same distance from everything else. Give related things less space and unrelated things more, and the page starts to explain itself.
Try it now: double the space between your sections and halve the space between a heading and its paragraph. Refresh. That's usually the whole fix.
Type
One typeface, two sizes for headings, one for body. A code snippet where a setting matters:
body { font-size: 1.0625rem; line-height: 1.55; max-width: 62ch; }“If you can't explain why an element is where it is, it's probably in the wrong place.”
Colour
Section body.
Alignment
Section body.
Restraint
Closing section. End with the one thing to do next.
