General Tips you say? Well tip one get better at Rattlers before trying a harder snake like a Garter....LOL Just kiddn
1. By all means make several casts of the head first of all, you will want it for study reference and will want it to set eyes and lip line and may need one for the actual form. Like these

2. I have found the easiest way to do them is to cast the whole snake using alginate by setting its pose and freezing it. Once its molded pour several casts using bondo/fiberglass resin. Then you can use one for the mount and have another for study or replica. Remeber you only have about a hour to cast in your alginate before it starts to dehydrate and break down. Should come out nicly like these. Other meathods are carve the form from foam or roll out magic sculpt and form it.... I have never carved a Colubrid ( just Pit Vipers ) nor do have experience with the apoxie method so these meathods I cant inform you on.

3. Plan on painting your eyes, get flints 2 or 3 mm from Van Dykes
4. Carefull on fleshing and scale stack cause they are not as durable as a Rattlers skin,
5. Take your time on the face ESPICALLY since its small, its like micro surgery and you will still screw it up most likly.
Im sure there is more to say but you just asked for a few tips......

Good luck and post it up when its mounted