Ok, I've just got to chime in here....
I was taught (by an amazing instructor) many years ago that you place the B/P cuff about an inch above the antecubital region (the 'front part' of the elbow), and the palpate the brachial artery, and place the diaphragm of the stethescope over it, and lightly press on the stethescope. Begin to inflate the cuff until you cannot hear any 'thumps', and then increase the pressure 30 mm/hg. S-L-O-W-L-Y start to release the pressure in the cuff.
As the pressure is being released, you will hear the pulse return, this will be your systolic pressure.
As you continute to release the pressure, you'll end up 'losing' the pulse sounds. This will be your diastolic pressure.
I will defend the use of the Sprague type stethescopes. I find them easier to hear with (especially in noisier situations). It is my personal choice.
If you ARE using the Sprague type, remember the head of the stethescope will turn. I use the large diaphragm for lung sounds and blood pressures. Remember that there is a 'flat side' of the head fixture. This indicates which diaphragm is 'turned on'. This 'flat side' will be toward your patient.
When using a stethescope that is 'single lumen', remember to keep your fat little thumb off the back of the head. I've noticed that those stethescopes are notorious for picking up YOUR pulse sounds from your thumb.
Also remember that if you take a blood pressure in the left arm and aren't sure of what you heard, if you inflate that cuff again, you'll get a different reading than you initially had.
I've seen people who inflate the B/P cuff to a minimum of 250 mm/hg or more rather than the correct way, and I want to auscultate a corotid B/P on them! It's not the proper way to do it, and causes the patient undue discomfort.
As has been stated before, the earpieces should be comfortable and fit the ear canal, and the 'arms' on the stethescope shoud be angled slightly forward. This directs the sound into the ear canal, and you don't try to rush though the process because the ear pieces make your ears hurt.
Practice is the key here. As you start practicing, do it in relatively quiet places, and then start to work with more noises (television, radio, other people talking; etc). This will help you hone the skill and be able to work in environments that are less than 'dead quiet'.