Now 90 years young, the Oracle of Omaha is still impressing with important life lessons.

Ever read something Warren Buffett said or did and mumble to yourself, "Why didn't I think of that?"

Outside of Buffett's mastery of investing, his down-to-earth wisdom is not only legendary but we all nod in agreement with the simple and yet profound effect it has on our lives.

Take, for example, the advice below. Common sense, yes. But to many of us, it's not common practice. That is, until we become believers that the principles actually work. All you need to do is act on them with positive intent.

1. Pick your friends wisely.

Buffett has taught so many lessons appealing to our common sense. One of them was recently highlighted in Bill Gates's memorable 90th-birthday message to his close friend: "Of all the things I've learned from Warren," said Gates, "the most important thing might be what friendship is all about. As Warren himself put it a few years ago when we spoke with some college students, 'You will move in the direction of the people that you associate with. So it's important to associate with people that are better than yourself. The friends you have will form you as you go through life. Make some good friends, keep them for the rest of your life, but have them be people that you admire as well as like.'"

2. Go to bed a little smarter each day.

The fact that Buffett has achieved so much means his advice is highly sought after. He thinks anyone can do the same if they follow one simple rule: the Buffett Formula.

According to Buffett, the key to your success is to go to bed a little smarter each day. Buffett pointed out the strong similarity with investing when he said, "That's how knowledge builds up. Like compound interest."

One of the ways he famously builds his knowledge is to read. A lot. While Buffett has been known to spend 80 percent of his daily routine reading, whether or not you have time for such an ambitious goal is largely irrelevant. The point of the Buffett Formula is to make whatever progress you can and improve your life on a daily basis.

3. Improve your communication skills.

"The most important investment you can make is in yourself," said Buffett. That includes personal and professional development to propel you forward in life and business. 

Buffett invested in improving his capacity to communicate better at an early age, which he said would increase your worth: "One easy way to become worth 50 percent more than you are now at least is to hone your communication skills--both written and verbal." 

4. Say no.

Buffett learned a long time ago that the greatest commodity of all is time. He simply mastered the art and practice of setting boundaries for himself. That's why this Buffett quote remains 

a powerful life lesson:

“The difference between successful people and really successful people is that really successful people say no to almost everything.”

As busy leaders and entrepreneurs, we have to know what to shoot for to simplify our lives. It means saying no over and over again to the unimportant things flying in our direction every day, and remaining focused on saying yes to the few things that truly matter.

Inc