What point should I start being real careful with the knife in order not to puncture bladder or poop sack.
You should begin being careful with the knife as soon as you take it out of it's sheath.....
There as many ways to field dress a deer as there are calibers of deer rifle, I think ..... hell, I have seen goobers on youtube shoot a deer and drag the whole thing, guts and all, back to their garage to do the "field dressing"...... makes me wonder how they missed the "field" part ......
There are a bajillion youtube vids on how to do this stuff .... but field dressing is so simple:
1. Make sure the animal is dead. (I have seen a grown man thrown a considerable distance when he grabbed the antler of a "dead" mule deer. It looked painfull, and my tender young ears learned some new, very confusing collections of words that day....) Touch an eyeball ... if the animal blinks, he ain't done yet.
2. Cut the throat under the jaw. Really cut it. You want to sever the windpipe, esophagus, jugular, carotid, ALL of it. I find it is easiest to find the cervical spine and stab through, and slice/saw out away from it.
3. Flip the deer over on it's back, head uphill, if possible. Grasp the um ..... penis sheath (or udder if it's a doe) with the left hand (assuming a right handed hunter here- lefties reverse) and pull the thing to the left, tightening the skin next to it ..... slice with blade down to make a small hole through skin.... hair will dull the edge very fast, so as soon as you have a hole through to the intestines, turn the knife (and your hand) over so that you have the edge up and the point between your pointer and insult fingers, and the hilt on your upturned palm. Unzip the skin and abdominal muscles from the inside, going up the midline, leading with your fingers so you don't poke any innards, up to the sternum, and down to the rectum (butt-hole, for those oy you in Rio Linda), taking care not to cut the urethra (pee-tube).
4. Split the pelvis. There are several ways to do this (and some folks don't do it all, carefully cutting around the rectum and basicly doing a butt-ectomy) .... I slice down to the bone and then drive the knife through the pelvis with a hatchet .... some use saws .... there's even that stupid "Butt-Out" anal rape tool to rip the rectum out ..... but I feel it defeats the whole purpose, which is to take the guts out without tearing them open and spilling their oh-so-appetizing contents on your meat..... anyhoo, get the rectum out from under the pelvis ....
5. Go back up to the sternum. There will be thin wall of muscle (the diaphram) separating the guts from the chest cavity, containing (if you placed your shot right) a bloody mess that used to be heart and lungs. Cut this out ( you can make fajitas out of it- marinate in lime juice, salt, cumin and peppers of your choice) all the way around the rib cage.
6. Now the hard part: roll up you sleeves (or take the long sleeved layers off entirely- on a large deer, you are going to get bloody up to yout shoulders!) and reach up in there and grab the windpipe .... it'll be clear up in the neck. Put a kink in it (bend it 90 degr) so it won't slip, an PULL! (It will help if someone pulls the other direction on the antlers or forelegs). PULL! Rip the lungs right outa that sucker ..... keep on pulling and the guts will follow, until the anus peels right off at the base of the tail. On older deer, you may have to make a couple of minor cuts to connective tissue to pull the lungs and intestines free .....
7. Lift the front end to dump any blood in the body cavity out the back end...... drag carcass to truck, hang it and wash the inside out- blood spoils quickly. Cool the carcass ASAP (not usually a problem in November in Nebraska.......).
After you do it a few times, it takes longer to tell it than do it ......