Overuse of Punctuation
Excess punctuation should be left out of most sentences on the web. If a reader sees a sentence with more than one comma, the sentence becomes harder to scan and therefore more likely to turn a reader off. More advanced punctuation such as semi-colons and colons should be avoided completely by starting new sentences instead.
Wrong: “It is really important to keep three principles in mind, when thinking of the best shoes to buy; comfort, style, and eco-impact.”
Right: “Comfort, style and eco-impact should be kept in mind when thinking of the best shoes to buy.”
Short, sweet and no semi-colon.
Follow AP Stylebook. In a series of three, use only one comma. Example: There are nursing, automotive and computer students in the hallway.
Capitalize Words in Headlines/Titles/Headers/Subheaders
Excepting prepositions (of, to, for, etc.) and the words "is", "and" and "the," all major words in a headline/title/header/subheader should be capitalized.
One Space After a Period
The convention for web writing is one space after a period.
Don’t Begin Sentences with “But”, “And”, or “Yet”
This is more common than you would think. If you are challenging a concept from the previous paragraph or sentence, you may use “However” to start the sentence. If you are trying to follow up on an idea from a previous sentence, don’t begin a new paragraph and just present the idea in the next sentence. Your audience will leap with you without an introductory “and” or “but”.
It’s Versus Its
This is a very common mistake that a lot of people make. "It’s" is short for “it is”, so “it’s all relative” is correct while “it’s color is blue” is not. “Its” is a term of possession, so “its color is blue” is correct.