There are some special characters that are used quite often. Below some examples of the most common special characters and the rules how they should be used.

Degree sign ° (Alt+0176) - should be used like 21° C (number-degree_sign-SPACE-unit_symbol).

In mathematical equations signs like <, >, +, - and = always should have a space before and after. You can put a non-breaking space before and after those characters. Best is to use math equations software in order to generate the right output.

Plus/minus sign ± (Alt+0177) should be used like 21.0 ± 0.2 (space before and after).

Percent sign "%" should always follow a number without any space beetwen, i.e.: 10%, 12.3%.

The multiply sign "×" (Alt+0215) should be used when i.e. writing dimensions 20×30 cm (do not use letter "x").

Choose Greek and other alfabet signs from the character map. DO NOT place a latin letter and change the font to "Symbol" - it's a risk that you'll have i.e. "u" instead of "μ"! The same refers to arrows and other symbols which are not a "regular" character.