These 26 key rules from Butterick’s Practical Typography might be the most useful listicle I’ve seen in years. A sample:

1. The four most im­por­tant ty­po­graphic choices you make in any doc­u­ment are point size, line spac­ing, line length, and font (pas­sim), be­cause those choices de­ter­mine how thebody text looks.
2. point size should be 10–12 points in printed doc­u­ments, 15-25 pix­els on the web.
3. line spac­ing should be 120–145% of the point size.
4. The av­er­age line length should be 45–90 char­ac­ters (in­clud­ing spaces).
5. The eas­i­est and most vis­i­ble im­prove­ment you can make to your ty­pog­ra­phy is to use a pro­fes­sional font, like those found in font rec­om­men­da­tions.
6. Avoid goofy fonts, mono­spaced fonts, and sys­tem fonts, es­pe­cially times new ro­man and Arial.

My number one rule for this blog is “Pick a template and don’t deviate” since I figure someone much better at this than me spent a lot of time thinking about how it should look.