There is a bit different in spoken and written; and that is due to the ascents. What we write in a sentence is quite same in comparison to British and American style. However, while speaking the words appear unique in British ascent, American ascent, Australian ascent, Asian ascent, etc.
As a common we always write 'I want to go' while speaking it we say 'I wanna go'. There is no such meaning of 'wanna' to write in a sentence; but while speaking people use nowadays.
Grammar is a part of spoken English. Before learning spoken English we must know the grammar part very well. However, while learning English it is not essential to learn the spoken skills. English grammar is being taught since lower classes in every school; due to which people little bit knows about the tenses, verbs, nouns, adjectives, prepositions, etc. So, written English classes are not required as spoken English is.
'Every bad situation will have something positive. Even a dead clock shows correct time twice a day.'