A synopsis is single spaced with a one inch margin framing the text. There is a blank line between each paragraph. When writing a synopsis, use the present tense. Yes, this can be tough when writing about past events that affect current happenings, such as a person who is dead and their thoughts or actions prior to dying. Also, remember that the first time a character is mentioned in a synopsis, write their name entirely in caps. Revert to normal formatting with subsequent mentioning of that character. Give a whitewash of the entire plot in an engaging manner. Tell the ending! Share what motivates your main characters to act and react the way they do.
Some experts suggest that as you write, open another document under the heading of "story highlights." When you've completed a chapter, write two or three sentences about the chapter in your file of highlights. For example, Vicky goes to the doctor for flu symptoms only to find out she is pregnant. Too bad she can't recall ever having sex. Of course there was that time her drink at a party tasted bitter, and she woke up in a strange bed.
Once your novel is completed, you can uses the gems you've written in your highlights file to craft your synopsis. Gee, this sounds so simple; WHY aren't I doing it? Because giving advice is always so much sweeter than taking it.