Always write as if the action of your novel were taking place before your eyes on a brightly lit stage.  This was the advice of Ford Madox Ford;  I keep it in mind all the time when I’m working on a novel.  It is the most important of my working rules.

Break all the others and with luck and talent you can still be published… Break Ford Madox Ford’s rule and you’re finished before you’ve begun.

The next example of how not to write is the one quoted by Graham Greene: “He got up, went downstairs, and hailed a taxi.”  You should memorize this and test every sentence against it.  If any has the same flat, dead quality, rewrite or cut it.  You must always act on the assumption that one such sentence will ruin the whole novel.