Use of contractions - Many people use contractions in their writing (shortened versions of words); these are not considered to be formal. Make sure you use full words.
don't X - do not
won't X - will not
can't X - cannot
Use of vocabulary - Remember there is a difference between formal and informal vocabulary - some words just should not be used in your writing. Yes, you must use synonyms but make sure that the synonym you use is not classed as 'colloquial' (spoken, informal).
mates X - friends
kids X - children
lads X - boys
Use of abbreviations - Again, you should use the full versions of words and not the shorter ones.
uni X - university
tele X - television
dept. X - department
Use of exclamation marks - The punctuation symbol ! should not be used in your formal writing, It is very emphatic and should only be used in stories and informal writing.
There was a huge change! X There was a huge change.
Use of spoken expressions - There is a tendency to use expressions that we use in presentations or spoken English.
Let's move to... X
Moving on... X
Now, let's talk about... X
Vocabulary:
will be considered = will be thought of as
classed as = put in the category of, seen as
colloquial (adj) = spoken, informal
version (n) = form
emphatic (adj) = empasised, dramatic
a tendency (n) = habit, typical way