Field dressing is pretty simply, a Google search will turn up all kinds of information.
If you have a gut hook on a knife, use it, makes opening them up about like pulling a zipper. Also, work with a sharp knife, it will make the job much easier.
If you're going to have the head mounted though, my rule of thumb is to stop my cut at the breastbone, that will leave plenty for the cape. If I don't plan to have the deer mounted I cut through the breastbone, just makes it easier to get to the esophagus and windpipe.
A small saw also helps to cut through the pelvic bone if you go that route.
If you puncture the stomach, intestines or bladder, wash the area with water if you have it.
Best of luck, after you do your first the rest will seem easy.
“There are two spiritual dangers in not owning a farm. One is the danger of supposing that breakfast comes from the grocery, and the other that heat comes from the furnace.”