Example for informal writing:
You know that book I wrote? Well, the publishing company rejected it. They thought it was awful. But hey, I did the best I could, and I think it was great. I´m not gonna redo it the way they said. (http://ezinearticles.com, 2010-04-20)
Example for formal writing:
It will be argued that the benefits of immigration outweigh the disadvantages. (http://www.ncistudent.net/studyskills/Writingskills/ , 2010-04-20)
Guidelines to informal writing:
- May use slang or exclamation makes (!).
- Use abbreviated words (photo, TV etc.).
- Use contractions (can´t, won´t etc).
- Address the text (you, your, yours etc).
- Use short or simple sentences.
- Use colloquial words/expressions like guy, kid, awesome, awful etc.
Guidelines to formal writing:
- Focus on the issue, not the writer.
- Use longer and more complex sentences.
- Use full versions of words (photograph, television etc).
- Write out full words (cannot, will not etc).
- Write to a large audience, no specific address (the reader, one etc).
- Avoid colloquial words/expressions and write instead boy, children, wonderful etc.
My own topic: Volcanic eruptions
Formal: A volcanic eruption has occurred on the island of Iceland, west of Sweden, last week. All plane traffic across Sweden, Denmark, Norway and the United Kingdom has been cancel, so there is no traffic in the air. All tourists there are on vacation have a hard time to come home. Many people has been forced to remain there they are and wait for the eruptions to subside.
Informal: O my God! A terrible thing has happened, thousands and thousands of holidaymakers are stuck. On Iceland there has been a volcanic eruption and no play´s are flying over Sweden, Denmark, Norway or the UK. So no one can come home! It can take weeks and weeks before the plain´s are up and running again. A car drive from Greece to Sweden takes a while to finish but i an option.
That´s that for today and this week. /L

Nice work Linda! Your lists of formal/informal guidelines are absolutely excellent. (Spelling: "exclamation MARKS")
SvaraRaderaJust a few things in your introduction:
"Informal and formal writing RELATE TO the style of writing, the way we use words AND sentences to express ourselves."
"Formal writing is used for academic texts"
"Tone, syntax and vocabulary ARE the main things THAT DISTINGUISH THESE two types of writing FROM EACH OTHER."
Formal text:
"has been CANCELLED"
"all tourists that are on vacation there"?
"Many people HAVE been forced to remain WHERE they are..."
Informal text:
"... no PLANES are flying... the PLANES are up and running... " (plural -s, no genitive apostrophe)
"but (it) is an option."
Well done!