Acquiring or developing gear that can communicate trends in the state
you wish to influence without being too disturbing is the first step.
Then you sit down and relax with no interruptions for a hunk of time.
Start with very few expectations and let your mind wander, or
meditate--different people get results different ways. But keep part
of your attention on the signal from the gear.
Any other person present should be someone who won't contribute
disturbance, but can cue you about external stuff--make an agreement
about whether this should be done during or after the session.
This can be particularly useful, for instance, when trying to influence
brainwave states--otherwise you may be training some scalp or eyelid
muscle(s) instead of affecting your EEG.
I taught myself to raise and lower my hand temperature(s) independent
of one another in something like 8-10 hours of 20-minute sessions.
Pulse control took longer, and I still find it a lot easier when I'm
off caffeine than when I'm on it. I assume it's blood chemistry related, but
there may be a cognitive component as well.
I never did much with EEG. I'm interested in BP, which is rumored
to be harder.
The model I have for how it happens is that I treat the signal (let's
say it's a continuous tone) as an itch I vaguely want to scratch, or
a muscle I kind of want to stretch. If I don't get into a relatively
"don't care" frame of mind, I can blast myself right out of the state
due to excitement, not unlike dropping the balls in glee the first
time one juggles, or popping out of lucid dreaming when you notice
you're doing it.
Yeah, I know it's vague, but remember you're trying to turn an
"involuntary" aspect into a "voluntary" one. No surprise that the
words aren't there... :)
MMB, at but not for OCC