Give your writing room to breathe
When writing, you have the writing part and you have everything else. We tend to undervalue the everything else to focus on the writing, agonising over word choice, sentence structure, and grammar while ignoring how the words look on a page. The everything else on the page is paragraph size, italics, bolding, line spacing, text alignment, font, size, link colour, orphans and widows and rags, margin size, and headings.
The everything else is powerful. It's the dry shampoo of writing, the pair of jeans that always look good, the easy but impressive dish you whip up for dinner parties. Even when you're not feeling confident about the writing part, if you've got the everything else working, you can probably bluff your way through. And when you are confident about the writing, everything else guarantees your wonderful words get the attention they deserve.
Spacing is a big part of the everything else. The aim of spacing is to help your reader consume your words easily. Spacing can be manipulated anywhere - a blog, an email, a text, a report, a hand-written note. It can be very overwhelming for a reader to see a big page of unbroken text. Instant turn-off.
Good spacing lets your words breathe, lets your reader's eyes relax and recover as they move through your words, and helps them take in your message. Plus it's free so don't be shy about hitting that enter button.
Paragraph size
Small paragraphs are better for comprehension. Ignore what you learned in primary school about PEEL (point, evidence, explanation, link) and break those long paras up.
Aim for three or four sentences per paragraph. If you can, make your paragraphs narrower when designing, say, a blog page. Both of these tips are taken from print journalists. You'll notice on the front page of a paper, the small print is offset by skinny columns and very short paragraphs to help people comprehend dense information.
Line spacing
The vertical distance between the line above and the line below is called line spacing. You might be used to either single-spaced or double-spaced line conventions thanks to Microsoft Word but line spacing exists on a gradient. Double-spaced is often too much; single-spaced is often too little. If you have the ability to toggle your line spacing, use it to your advantage - get some breathing room in between your lines.
Bullet points
I spoke to someone recently who despised the use of bullet points. She said using bullet points made her think the writer was lazy, rude, and stupid. The counter-argument I loudly made for bullet points is that they rule and SHE is the one who is rude! Also, bullet points are perfect for:
itemising key pieces of information
cutting down on formal sentence structure and getting straight to the point
pulling out key pieces of information so they're visually separated and stand out
helping readers parse information quickly
Use bullet points liberally to highlight key parts of your message. Format bullet points consistently, such as using all full sentences or all fragments, all with full stops or none with full stops.
Alignment
Centre alignment should be reserved for short titles or image captions, otherwise, try to stick to left-aligned text. This becomes a bit unfun when you're designing a website because centre alignment looks better and designers love it. But text is harder to read when centre-aligned because the eye doesn't have a fixed point to return to. A long paragraph of centre-aligned text isn't kind to the reader.
TL;DR? Give your words room to breathe for better comprehension. Aim for short, narrow paragraphs, play with line spacing, liberally apply bullet points, and stick to left-aligned text.