What do you find it to be the most important thing

This is a tough question.  For a newcomer the most important thing is to use more lube than you think you’ll need.  Then add more. While I stand by that statement it won’t necessarily get someone very far past insertion….

The more tightly you grip it, the more it slips through your fingers like sand. I'm sure I read something like that here years ago, but it doesn't really hit until you encounter the truth of it first hand.

That's the single most universal truth I've gathered in my ~16 years of doing this. I'm still battling my own definition of what "surrender" and "relaxation" means... and I'm still surprised by how far I fall short, and how often. I've reached a point where the contradiction is slapping me in the face with its truth. The good-feeling involuntaries are only possible with pelvic relaxation, and mental surrender. Attempts to push and press for repeats of these contractions are a trap, because it was never the contractions leading the pleasure, it was pleasure leading the good-feeling contractions.

It took me a long time to finally learn to be totally relaxed! That means to learn to relax the anal sphincters as well as the rest of the body! When one learns to do that, then progress will happen! You will experience the tip of the Aneros as it stimulates the prostate and begin to move on its own followed by intense pleasure and then progressively into Os and super Os!

The giving in part is what I consider important. Figuring out what you are giving into. I’m amazed when I let go, let the device do the work at how good it feels, how hard my cock gets and how long it stays hard. I mean like it could rupture hard. I close my eyes and picture what the device looks like and what it is doing. It honestly feels like the device is running up thru me and is up inside my cock. It’s like it is all one piece. This may sound strange but when that thought started in my head I got really hard. When the auto kicks in, I’m getting audible by this time. There is no finish to it. Just enjoy the time these kind of orgasms come and go. Now you can have a finish if that’s what you like but it will reset your brain by design to starting over. I have found my inner thoughts to be the most productive at arrousing myself. Other things tends to be a distraction. I close my eyes and let my imagination do the work.

That must be relax.

Don't think anything about orgasm. Just like lying in a boat floating in the middle of a lake. Keep contract PC muscles and deep breath even feel some special sense. Don't try to catch the orgasm(but use some trick to enhance the feeling, such as hold breathe shortly and tighten PC muscle strongly for once, is OK), it will walk to you naturally.

Relax. More. You may think you are relaxed but you're not. Try to relax to the point you barely notice the device, it should "float" inside you. It's one of the reasons I think smaller devices work so well. Took me 10 years and little THC to realize that, since everything clicked.

I'd say that mechanically speaking, the most important thing is to position your body so that you can be relaxed and breathing freely, while making sure that the Aneros has maximum mobility. 

Id say for me its letting go....letting go of muscle tension and letting go of mental expectation. Expect nothing and enjoy everything. Way harder than it sounds!

Single most important thing for me seems to be a RHYTHM!

All of what people say about relaxing, deep breathing using the stomach expelling air out and deep breaths to expand the stomach, and so on I do start that way.  I will also tease erogenous zones like the inner thigh, around my belly button, up to my chest and then save gently rubbing my nipples with thumbs in a circular motion for closer to the end.  

But as far as what really gets things revved up would be a rhythm of thrusts like a rocking motion of my hips so that the ‘toy’ does a gentle tapping (reminds me of when people use an NJoy wand to rock against the p-spot). The rhythm is slow at first but then this in combination with self touching everywhere but the penis allows me to start feel things warming up.  I start to breath heavier or let out a few little moans.  I close my eyes (sometimes open to see myself) and the whole time with earplugs to block out exterior noises - similar to sensory deprivation.  The warming up keeps building and I will feel my body knows how fast I want to hump/thrust and I’ll feel more going on with the toy tapping.  The building keeps increasing and it’ll be more akin to crashing waves.  You might get a larger wave that feels like it will be big but then it’ll settle down to a calmer wave still pleasurable.  But keeping up the ‘tap tap tap’ rhythm will make the waves start becoming bigger until finally there is the one that just sends you into “orbit”.  It’s about this time I’m rubbing my nipples with jittering hands and I can’t control my incredibly loud screams of pleasure.  Moans become more of a bark/growl and it just seems like I’ve lost all control and the pleasure is taking pure control of me.  It does seem like it can go on forever and the longer it lasts the more intense it gets.  It’ll settle down again but if you keep up the rhythm multiple orgasms can happen which for me they do.  Definitely the ‘lost sense of time’ becomes a factor and I’ll realize 2+ hours went by where I was just in pure ecstasy/sexual bliss.  

So definitely rhythm for me is the common factor for every (IMO) super-O.  It seems pretty consistent for results as I have done this 2-3 days in a row and each time different but equally satisfying.  Find a way to stabilize the toy (pillow wedged) while slightly inclined that you like and “ride” it like you’re on a horse changing the “trot” bump speed.  At some point it’ll just feel like you’re banging against the toy in a frenzy too, that’s normal.  As for a specific toy all I know is I like large/thicker more fuller toys.  Feel free to ask if you want to know the specific ones I have come to love.