English language has the following two broad components:
Grammar : The accuracy and the correctness of the construction.
Vocabulary : Usage of a precise word to convey what is meant.
These are common to both spoken and written English. Once these are achieved, then based on the requirement, spoken or written various other aspects come into play. Depending upon the nature of usage, personal or professional, these get modified. At all times it is helpful to remember that Written and Spoken Language are two sides of communication. These are unique and effective in their own way. Each comes with its own set of advantages and limitations. Once we understand these the language becomes a means of effective communication.
In Written communication the choice of words, correctness of the construct, punctuation gain importance. In Spoken communication, in addition to the vocabulary and grammar, tone of voice, intonation clarity of speech, fluency etc. gain importance. Written communication is relatively slow paced. It offers time to ponder and choose. Spoken communication is spontaneous and hence needs more caution.
That is for now. The discussion will continue.
Have a good day.