Abbreviations are shortened versions of words or words replaced with symbols. Here are some common ones that you might find useful:
Some examples of abbreviating
Vowel deletion - but be careful to avoid ambiguity i.e. ct could be cat, cot, cut etc.
Endings or beginnings can be deleted - again avoid ambiguity i.e. underst could be understanding, understated etc.
Syllable deletion cuts out any part of the word that seems redundant i.e.purpose becomes purps.
Initial letters for technical terms, common phrases as well as for repeated authors and titles etc e.g. GCSE, TQM, WS (William Shakespeare) etc.
Symbols - either standard ones or of your own making.
Q - Question
C20 - 20th Century
But develop your own as well. Think of the ones you use when texting!