1) Know the font's personality.
Every font has a personality. And people like some personalities better than others. So what the rule here? Know your audience, know your document's purpose, and pick a font that matches your audience's expectations and your document's purpose. Get this rule wrong, and you have ruined the entire document.
2) Avoid the default fonts.
If you use the default font in Word or InDesign, you are telling the world that you didn't know there are any other options. Times New Roman and Calibri are not a bad font. They are just overused. Go back to Rule #1 and think about personality. Could there be something better than the default? In most case, the answer is yes.
3) Use two fonts.
Most documents look better if you use more than one font. But few look good if you use more then three. So what do you need to remember? No matter what the document is, try using two fonts, one font for the heading and another font for the body text. It will make you document pop so much more than just using one. This rule applies to all documents, from proposals to website layout design.
4) Contrast font families.
While it is good to use two fonts, it is bad to use two fonts that look like each other. So pick two fonts that come from different font families like (Times New Roman), san safari (like Arial), script (anything that looks like handwriting), or decorative. Make sure fonts look very different from each other.
5) Don't use all caps.
We read words in shapes. That's how our brain reads so fast. But when we write words in ALL CAPS, the shapes go away-words all turn into rectangles. So when you write out a bunch of words in all caps, it slows down reading. To the person reading, all caps also looks like you're yelling at them.
6) Be careful with reverse type.
Reverse type means you put a light color of text on a dark background or vice versa. Reverse type is good for headings and titles but not much else. If you use reverse type, be sure to have highly contrasting colors, never use blue on red, don't use fonts with narrow or fancy features, and use fonts with heavy weights.
7) Adjust your line spacing.
Line spacing, also called leading, is the space between lines. Most often, fonts are designed with line spacing slightly larger than their point size (if you have a 10-point font, the default is probably 12-point leading). Typically, that looks crowded with large bodies of text. Consider increasing line spacing to improve readability (but don't' increase it too much).