There are three main types of sentence in English: simple, compound and complex.
Simple
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Registration begins on 14 September. |
Compound
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Registration begins on 14 September but courses do not start until 1 October. |
Complex
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Although registration starts on 14 September, courses do not start until 1 October. |
Well-written texts will contain sentences not only of all these three types but also of different lengths. Although short sentences are more understandable than long ones, avoid a telegraphic style by writing short, medium and (sometimes) long sentences. Aim for an average sentence length of between 15 and 20 words and beware of excessively long sentences with too many subordinations and parenthetical elements.