First time parent with twins on the way.
I know you’re busy, so feel free to ignore this as I will eventually learn and come to my own conclusions.  I do, however, trust and value your advice.
Congratulations and Good Luck!

Aside from standard practices on raising children, is there anything else that you feel is important to expose them to? 
When Nate was born, I posted Rudyard Kipling’s poem “IF”(1) on his bedroom wall and soon I will give him the copy of Desiderata(2) my father gave me.

Keep them away from?
Nate has my 3 Rules of Life memorized: Live Smart, Avoid Dumb, Don’t Sabotage. He knows that he was born into a family that – Reads Books v. Watching TV, Takes the Stairs, Not the Elevator, Plays Sports v. Watching TV, Eats Healthy (Veggies and Fruit), Avoids Fast/Processed Foods, and Everyone Packs their Own Weight (terminology is from backpacking/hiking). He also knows – To whom much is given, much is expected; with great power, comes great responsibility; hard work beats genius when genius doesn’t work hard.

I notice that you frequently put puzzles and books up for grabs.  What about teaching children things like delayed gratification, concentration/focus, risk calculation, pushing one’s self past self-imposed limits, self-reliance?
Our best sermons are our own lives, the coping mechanisms we demonstrate when we are under stress or weary, our responses to life’s inevitable challenges.

Teach and demonstrate the value of planting acorns?
My dad was open with us kids about family finances and I’ve attempted to do the same. I’ve told him life is like an apple, both limited and limitless. Today, it’s just an apple. Plant the seeds, tend them carefully, and before long you have an orchard.

How do you feel about exposing children to technology such as smart phones or tablets?
Kids do need to be technologically literate; Nate has had an iPad from a young age BUT with VERY limited screen time (he claims he has by FAR the least of any of his contemporaries). We make exceptions for trips, scientific documentaries and books on Kindle. We have at times given him a basic cellphone to carry for communication emergencies; a smart phone a few years in the future (he is 11 and a half now).

Footnote 1. “If” by Rudyard Kipling

IF you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you,
But make allowance for their doubting too;
If you can wait and not be tired by waiting,
Or being lied about, don’t deal in lies,
Or being hated, don’t give way to hating,
And yet don’t look too good, nor talk too wise:

If you can dream – and not make dreams your master;
If you can think – and not make thoughts your aim;
If you can meet with Triumph and Disaster
And treat those two impostors just the same;
If you can bear to hear the truth you’ve spoken
Twisted by knaves to make a trap for fools,
Or watch the things you gave your life to, broken,
And stoop and build ’em up with worn-out tools:

If you can make one heap of all your winnings
And risk it on one turn of pitch-and-toss,
And lose, and start again at your beginnings
And never breathe a word about your loss;
If you can force your heart and nerve and sinew
To serve your turn long after they are gone,
And so hold on when there is nothing in you
Except the Will which says to them: ‘Hold on!’

If you can talk with crowds and keep your virtue,
‘Or walk with Kings – nor lose the common touch,
if neither foes nor loving friends can hurt you,
If all men count with you, but none too much;
If you can fill the unforgiving minute
With sixty seconds’ worth of distance run,
Yours is the Earth and everything that’s in it,
And – which is more – you’ll be a Man, my son!

Footnote 2. Desiderata by Max Ehrmann

Go placidly amid the noise and the haste, and remember what peace there may be in silence. As far as possible, without surrender, be on good terms with all persons.
Speak your truth quietly and clearly; and listen to others, even to the dull and the ignorant; they too have their story.
Avoid loud and aggressive persons; they are vexatious to the spirit. If you compare yourself with others, you may become vain or bitter, for always there will be greater and lesser persons than yourself.
Enjoy your achievements as well as your plans. Keep interested in your own career, however humble; it is a real possession in the changing fortunes of time.
Exercise caution in your business affairs, for the world is full of trickery. But let this not blind you to what virtue there is; many persons strive for high ideals, and everywhere life is full of heroism.
Be yourself. Especially, do not feign affection. Neither be cynical about love; for in the face of all aridity and disenchantment it is as perennial as the grass.
Take kindly the counsel of the years, gracefully surrendering the things of youth.
Nurture strength of spirit to shield you in sudden misfortune. But do not distress yourself with dark imaginings. Many fears are born of fatigue and loneliness.
Beyond a wholesome discipline, be gentle with yourself. You are a child of the universe no less than the trees and the stars; you have a right to be here.
And whether or not it is clear to you, no doubt the universe is unfolding as it should. Therefore be at peace with God, whatever you conceive Him to be. And whatever your labors and aspirations, in the noisy confusion of life, keep peace in your soul. With all its sham, drudgery and broken dreams, it is still a beautiful world. Be cheerful. Strive to be happy.

As always, I share what I most want and need to learn. – Nathan S. Collier