rbattelle said:... 2. Punctuation.
The most common mark of punctuation is the period. Use this to end a sentence and signal the reader that a new sentence with a new idea is about to begin. Begin the next sentence 2 spaces to the right of the period.
A point of clarification: using two spaces after the period is a rule that applies to typing on a fixed-pitch typewriter (or using a fixed-pitch font). When using proportionally-spaced fonts, as is the norm in typesetting and on most web page displays, the rule calls for one space.