The most important advice
This is even more important as you achieve more and if you are in positions of power.
1. Treat others the way you would like to be treated
With a great deal of hard and smart work you can do almost anything. Professional sports and traditional high fashion model might be the only caveats.
2. You can do anything (within reason)
3. We don't all start at the same place, but you can overcome a lot
To push back on #2, look at this young man for inspiration. If he can be this good at wrestling what are you capable of that you are telling yourself "I can't."
If you are born in the western world, you don't have much to complain about. If you are whining that you didn't grow up with more money, or did not go to the finest schools, look at the young man above for inspiration.
4. You are not a victim
There are real problems in the world. Not getting into the school you wanted or not getting the job you want is not a real problem. Bad things do happen to good people, unfortunately.
Not only that, most of the uber successful overcame A LOT. It make the journey much more satisfying.
If you are born on third and get to home plate is that better than just hitting a double? Be proud of yourself. Don't waste much time complaining.
5. Listen/Observe more than you talk
Theory is great, in practice. Have a plan, but you only get good at something by doing. Then do some more and make adjustments.