Yeah I am definitely nervous about doing this and doing it right.
Here's a little (a lot) more advice...
DON'T PANIC as soon as you let off that
first charge
and the timer starts! You'll start panicking and hitting other asteroids and missing fissures! Launch your Prospector, identity that it's a Void Opal core. THEN, MAP OUT the fissures! It usually takes, in my experience, about two High, one average and maybe a low or two fissures to hit the sweet
BLUE spot on the charge graph (upper right HUD).
Just take your time, make sure your ship has PIPs to shields and a few to engines, don't sweat Weapons, but DO make sure your weapon PIP is fully charged up. Don't get TOO close to the asteroid, makes it harder to maneuver around it, but obviously don't be too far either. Watch your timer. When you get down to like 20 or 30 seconds, maybe then start backing off. I usually go back about 2.5km to avoid the "blast zone", but I have been caught in the blast and it's kind of cool actually. Your ship gets rocked a bit, a little "Sensor Disruption" but that's it. I have no idea what happens if you're TOO close though, might take out your ship but I don't know. You're going to panic at first and under charge or over charge, just the way it goes... but after a few asteroids you're going to be nailing the perfect blast! After the blast, open cargo and fly close to the asteroid (don't need to be too close but close) and let your limpets do their job. Watch your Inventory and make sure you have room to collect and it's not "Cargo Hold Full", you might need to dump a few limpets to make room, no biggie, just dump out about two or three, and just fill up. Many VO deposits will stick to the rock, so use your Abrasion Blaster to knock them off to get scooped up. OK, now, here's the best part, BUT this might have been NERFed today with the update... once you have collected ALL the VO chucks,
backup and keep the asteroid "SPOT" in the dead center of some aim function you have, use the Blaster or what you have that you can use to center where the asteroid is/was and backup until the asteroid field
resets. I would say, back up about a good minute or two, until you see the smoke and field RESET. You'll know it when you see it. As soon as it resets, fly directly back to where the asteroids was and it should, if they did not NERF it today, reset and be collectible again. No need to fly around looking for another Core, it will be right there, reset and good to blast again! I hope to GOD they did not NERF this, I'll know later tonight. Also, this is what I do, not sure about your ship. I find my spot, and find a nearby station. I keep all my mining stuff at that station. That way I have a close base. I outfit my ship, store what I don't need at the station, and go mine. Then I fly back to the station and unload all my mining gear, and put back all my combat stuff, so I can defend myself on my way to the sell spot. The only thing I can't do is outfit back my better and engineered shields as a cargo rack is in that slot, so I just use another slot for lesser shields, but avoiding an interdiction is easy, unless you're in OPEN, where you'll have little chance getting out of that pirate interdiction. I am offering you all this info because I almost gave up on Elite, was stuck not sure how to really make good money and then I found VO CORES! Now, I am a billionaire! Ha! And forget LTD Cores, VO's are worth more! You might want to practice on them, if you hit one before a VO Core though. Go for it! Practice makes perfect! Last bit of advice is this... When you find a VO that's spinning fast or has other asteroids very close, you might want to just move on and find another one where it's a slow spin and has more room to fly around it. Seems like they intentionally make the CORES spin a little fast and close to other 'droids, but you'll find the perfect one and you'll be thankful for it!

Enjoy the Billions you're going to make! o7
Here's a tool to find the best selling location. I use it all the time. Just make sure the "WHEN" column is not like 28 hours ago, find a spot in the list, that's reasonably close that has a reasonable "WHEN" time. I like the ones that say an hour or less.
http://edtools.ddns.net/miner