When I was 20-ish, I read the book "Life's Little Instruction Book". Worth a cursory read, or at least checking it out on the webz. Here were some of the best ones, and some of my own.
The only thing you have to do is breathe.
No matter what happens, unless you die, life goes on.
Get your priorities straight. No one ever said on their death bed, ‘geez, I wish I spent more time in the office.’
Keep your promises.
Do the right thing, regardless of what others think.
Don't expect life to be fair.
Strive for excellence, not perfection.
Evaluate yourself by your own standards, not someone else's.
Practice what you preach.
Don’t use time or words carelessly; neither can be retrieved.
Look people in the eye.
Good enough rarely is.
Don't allow the phone to interrupt important moments. It's there for your convenience, not the callers’.
Be modest. A lot was accomplished before you were born.
If something sounds too good to be true, it usually is.
When you only need to buy something once, buy the best.
Remember that overnight success usually takes about 15 years.
Never swap your integrity for money, power, or fame.
Don't undertip the waiter/waitress because the food was bad. They didn't cook it.
Be cautious about lending money to friends - you may lose both.
If you're not passing anyone, get the hell out of the left lane.
Get, and stay, in shape.
Tell everyone to "have a nice day", you'd be surprised how much they’ll appreciate it.
Remember that hearing and listening are two different things.
Never deprive someone of hope - it might be all they have.
Have a firm handshake.
If you don't feel comfortable giving your two best friends a key to your house, it's time to look for some new best friends.
Give people a second chance, but never a third.
Don't waste time with music you don't like. Spend the time with music you love instead.
When taking a woman home, make sure she is safely inside before you leave.
Don't be intimidated into doing something you don't want to, or not doing something you do want to.
When you say "I love you", mean it.
When you say "I'm sorry", look the person in the eye.
Don't believe all you hear, spend all you have, or sleep all you want.
Remember what's right isn't always popular, and what's popular isn't always right.
When shaking a woman's hand, never squeeze her hand harder than she is squeezing yours.
Send lots of Christmas and Valentine cards. Sign them "Someone who thinks you're terrific".
If you lend someone money, make sure their character exceeds the collateral.
Accept a breath mint if one is offered to you.
Be open and accessible, the next person you meet could be your best friend.
Everyone loves praise. Look hard for ways to give it to them.
Remember people's birthdays.
Be forgiving of yourself and others.
Take care of your reputation; it's your most valuable asset.
Learn to listen. Opportunity sometimes knocks very softly.
Every so often, push your luck.
Be quick to take advantage of an advantage.
Don’t risk what you can't afford to lose.
Watch your attitude. It's the first thing people notice about you.
Don't overlook life's small joys while looking for the big ones.
Give people more than they expect and do it cheerfully.
Check for toilet paper before sitting down.
Send cards for no reason whatsoever.
Send flowers for no reason whatsoever.
I'll come back another time with specific answers to your questions, but Orbert nailed a bunch of it... especially about time moving quicker. I don't know if that's a function of age, or having kids, but holy shit does time start to accelerate.