Here's a tip that NOBODY here has posted yet: palpate the brachial artery first. Seriously. Find the darned thing. If you don't know where it is, you very well could be putting the stethoscope in the wrong place. I've been doing manual BP stuff for YEARS. Like 20 years and thousands (about 20k) of measurements over that period of time, the vast majority during transport. Yes, I said transport. That's a very difficult environment from an acoustic perspective and most of the time I have been able to auscultate blood pressures.
When I'm doing manual BP's, I first place the cuff and then the very next thing I do is straighten the elbow out so that the vascular structures are going to be as close to the skin as possible. The next thing I do is immediately palpate for the brachial artery. It's usually medial to the biceps brachii tendon as it crosses the antecubital fossa area. While you're palpating that area, you might also note the median cubital vein or even the basilic vein... but what you're feeling for is the brachial artery. It's usually clearly palpable. Note the position and that's right where you want to place the head of the stethoscope.
Here's where I do things a little differently. Once I have palpated the artery, I inflate the cuff while palpating and note when I no longer feel the artery pulsating. Then I deflate slowly and note exactly when I feel that return. I make a mental note of this for two reasons: One is that I now know about where I should start hearing the Korotkoff sounds and two is that by doing this, I've taken a legally valid blood pressure. It's not as "good" but it's still legal. As soon as I have taken that BP, I deflate the cuff completely and that's when I place my stethoscope right where I felt that blood pressure.
You want to hold the head in place with gentle pressure that's firm enough to prevent it from moving about. I'm not saying you should crush the darned thing, you just use maybe two or three pounds of force.
Here's where I differ from most: I listen to the BP as I inflate. Usually I'll inflate to about 90 mmHg and then listen. If I don't hear the sounds, I'll inflate to about 120. If nothing, I inflate a little more. This is because some people have very high diastolic pressures and you won't hear sounds until you're above the diastolic. Remember, this is assuming the patient isn't hypotensive. In those cases, I just modify this by using lower pressures. Once I have "captured" the sound, I know what the Korotkoff sounds are like with that particular patient and I will then inflate the cuff until about 20 mmHg above the point where I palpated the systolic BP. Then I deflate slowly and listen for some very soft Korotkoff sounds. Once I hear that, I note it as that's the systolic. Then I'll deflate rather rapidly until about 30 or so above where I first started hearing the sounds and than I slow the deflate rate again and note when the sounds disappear. That's the diastolic number.
Using this method and either an ECG monitor OR a pulse oximeter, I can usually get a full set of very basic vitals (minus temp) faster than most NIBP machines can do it. Seriously, I can be that fast at it.
However, to ensure that kind of speed, I must palpate that brachial artery first. I have to know exactly where it is. Then I just make sure that everything else doesn't move or rubs against something else. The only things my stethoscope touch when I'm using it are the diaphragm, two of my fingers (I use the "V" method described above), and my ears with the stethoscope tips pointed right down my ear canals. The tubing does NOT touch anything as I position myself so the tubing is free-floating and the stethoscope head is NOT touching anything else. The steth head does NOT touch the patient's trunk, clothing, BP cuff, NOTHING. When I'm doing everything exactly right, I will hear only two sounds through that stethoscope. Kortokoff sounds or the sounds of my finger joints creaking. Those two sounds are very different and if I keep my fingers very still, I won't even hear the creaking.