Try to split long sentences into shorter ones. Shorter sentences make text easier to read. Use one space, not two, after full stops.
Never put two full stops in a row.
Never put a full stop after a web address as it will be thought it is part of the address.
Questions and exclamations
Use question marks and exclamation points instead of a full stop, not in addition to one, even in quotations.
Within brackets
A sentence that stands alone within brackets needs a full stop inside the parentheses with it. (Here is an example.)
A sentence in parentheses within another sentence does not take a full stop, because the full stop is reserved for the main sentence
(Questions and exclamations, however, must have their respective marks!).
Abbreviations
A sentence containing a parenthesis must itself have terminal punctuation (are we almost done?).
Finally, an abbreviation ending with a full stop that is immediately followed by a question mark or exclamation point requires both marks (Q.E.D.!).