What could a 20-year-old do to potentially improve their quality of life further down the line?

 The quality of your life is largely dependent on the quality of the people in your life. And the quality of the people in your life largely comes down to how you make people feel.

Somewhere along the line in my late 30's I came to the conclusion that the words we habitually use have the power to transform life into mostly an experience of peace, fun and positive human interaction...OR on the flip-side transform it into a searing cauldron of non-stop daily pain...a veritable hell on earth.
'Hell on earth'...boy have I experienced that - almost to the point of killing myself therefore...

I often think that we should go through a 'licensing period' before we are allowed to operate or open our mouth (just like we require a license to own a firearm) - because the words that often spring from an unthinking, untrained mouth can leave wounds that never heal, destroy trust that will never be regained and break families apart like a sledge hammer hitting a walnut. Mine included...

So that being said if I could roll back the clock to when I was 20 (or even younger) I would invest a large portion of my time learning how to speak to people in ways that build positive bridges between us. I would even go as far to say that I would like the majority of my words to be gifts to the recipients or at the very least (to steal from the Hippocratic Oath) "abstain from doing harm" as best possible.

Is this easy to do?

No.But what I have found is that, over time, you can train yourself to pause slightly before speaking you can mentally edit what you say...or even delete it before it leaves your mouth.

Is it worth the effort?

Absolutely, 110% YES! Almost everything we want or need in this world must come from other people...and all things being equal people tend to favor dealing with people they know, like and trust. Words are your tools to achieve these.

I want to finish up my answer with this little story that I fell in love with and I think you will appreciate too...

There once was a little boy who had a bad temper. His father gave him a bag of nails and told him that every time he lost his temper, he must hammer a nail into the back of the fence. The first day the boy had driven 37 nails into the fence.

Over the next few weeks, as he learned to control his anger, the number of nails hammered daily gradually dwindled down. He discovered it was easier to hold his temper than to drive those nails into the fence. Finally the day came when the boy didn't lose his temper at all.

He told his father about it and the father suggested that the boy now pull out one nail for each day that he was able to hold his temper. The days passed and the young boy was finally able to tell his father that all the nails were gone.

The father took his son by the hand and led him to the fence. He said, "You have done well, my son, but look at the holes in the fence. The fence will never be the same. When you say things in anger, they leave a scar just like this one. You can put a knife in a man and draw it out. It won't matter how many times you say I'm sorry, the wound is still there."

The little boy then understood how powerful his words were. He looked up at his father and said "I hope you can forgive me father for the holes I put in you."

"Of course I can," said the father.