The Elements of Style

you should be able to

As a rule, begin each paragraph with a topic sentence, end it in conformity with the beginning.

The beginning of each paragraph is a signal to him that a new step in the development of the subject has been reached.

there may be no need of

require a comma before the conjunction.

In this perilous situation, there is still one chance of escape.

Consequently, loose sentences of the type first quoted are common in easy, unstudied writing. But a writer should be careful not to construct too many of his sentences after this pattern

and an occasional loose sentence prevents the style from becoming too formal and gives the reader a certain relief.

Further, and is the least specific of connectives. Used between independent clauses, it indicates only that a relation exists between them without defining that relation.

The situation is perilous, but there is still one chance of escape.