A ‣ What is formality? 
Formality is all about your relationship with the person you're speaking or writing to. If you use formal language, it may be because you wish to show respect, politeness, or to put yourself at a distance (for example, 'official' language, or academic language). Informal language can show friendliness, equality or a feeling of closeness and solidarity with someone. You should never use informal language just to sound fluent or clever.
B ‣ Scales of formality 
Some groups of words can be put on a scale from formal to neutral to informal.
formal → | neutral → | informal |
offspring | children | kids |
abode / residence | house / flat / home | place |
goodbye | bye | bye-bye / cheerio |
go amiss | go wrong | go pear-shaped |
C ‣ Words of Latin and Greek origin 
Many longer words that come from Latin and Greek are quite formal. Here are some with their neutral and/or informal equivalents, which are often shorter words.
I'll go and email Kieran immediately. [neutral equivalent: at once; informal equivalent: right away]
The researchers utilise the most modern equipment. [neutral equivalent: use]
This problem frequently occurs with older software. [neutral equivalent: often happens]
The study established a link between stress and ill-health. [neutral equivalent: showed/proved]
This book provides us with a picture of ordinary life in the Middle Ages. [neutral equivalent: gives]
The government attempted to reduce unemployment by supporting new businesses. [neutral equivalent: tried]
Physicists seek answers to fundamental questions about the universe. [neutral equivalents: search for / look for; basic]
D ‣ Formal phrases 
Many phrases are typical of formal contexts such as academic or official language.
What should the government do in terms of1 helping young people? Students, in particular2, need support to complete their studies, on account of3 the high fees and living costs they have to meet. Should students be given financial support on the basis of4 their family circumstances? And how should the government act in relation to5 youth unemployment?
The definitions give less formal or neutral equivalents.
1 as regards, about
2 especially
3 because of
4 according to
5 as regards, about, in connection with
E ‣ Formality in notices, instructions, etc. 
You will often see rather formal words in signs, notices and directions. Make sure you know the meaning of the words used so that you could tell someone what the notice says using less formal words.
