What I use for serious work:
Protektor rear leather bag with bunny ears (the short ones) filled with #4 blasting sand and a cinder block front rest with a 25# cloth bag of shot on top. Cover both with wool varnish applicator pad (or sheepskin anything) to uniform the friction and prevent the rifle grabbing the bags.
I don't have an X bag (Caldwell makes a nice one) but have used them and may have to get one.
You must have a rear support and learn how to use it. Pound the butt into the bag hard, then put your face over the stock directly above the bag with your eye in a vertical line with the scope and drop your head straight down to "load" your chipmunk cheek skin fully against the top of the comb. If your eye won't line up, get different height scope mounts. Practice getting comfortable resting the weight of your head on the comb this way (always using only down force) and you can get a consistent 15 or so pounds of pressure straight down on the butt. Be careful NOT to load the stock sideways or fore and aft with your head. Did I mention to only apply downforce (mostly gravity) to the comb with your head? Ok, good.
Front rest needs the same pound-in as ITS mentioned. Keep your support hand off the rifle, use it to adjust the butt bag or just place the hand flat on the table or however feels comfortable. You may want elbow pads because they will get sore. Wool pads work well for elbows, too. Keep both feet flat on the ground and try to space the support bags relative to the table so that you are sitting mostly upright and not leaning over or across the rifle. When in position for the shot you should be able to relax your whole body and except for your shooting grip and stay in position. Any muscle force required to maintain position is a variable that can affect the shot or be subject to tremor. Now you get to sort out your breathing and trigger squeeze....and follow through. Never forget about follow through. Pull the trigger straight to the rear and hold it there until the rifle settles back into the bags after recoil. How much pressure you put on the butt pad with your shoulder will vary with rifle recoil and stock shape, but a light contact that can be maintained by ONLY touching the rifle with your shoulder and face is what I recommend unless recoil is so much that you risk getting scope cut.
Any small force you put on the rifle to hold the crosshairs on target will affect the shot. Fidget with things until the rifle is dead-on your aiming point with just the weight of your head holding it in place, then reach up with your firing hand, gently grasp the wrist, find the trigger, breathe, and break the shot. You may find it handy to place your firing hand thumb along the stock pointing forward instead of wrapped across the top. Thats all I got. You can read volumes on breath control so I'll let you sort that out for yourself.
