The most important thing IMO: look up real snake skin. Google images is a tremendous resource for reference pictures of this, or just about anything.
For that matter look up giant snakes: anacondas, pythons and things. Look at their proportions, shapes, even their poses.
If you want to sculpt it quickly, I'd say get your snake positioned, shaped, and cured; smooth your layer of putty over it (or over however much of it you feel confident in completing before the putty layer hardens); and press a criss-cross, 'quilted' diamond pattern into it. Maybe try to push down the front edge of each diagonal row, give more of an impression of overlapping scales. Either by using a flattish tool to push in each row at a slight angle, creating a stepped effect, rather than simply marking the edge of the row with a sharper edge; or, if marking with said sharper edge, go over again and smooth the front edge down. You might want to go over it again and give it some tweaks and refinement anyway, if you have the time.
Oh, and practise a small patch once or twice, before you move onto the snake.