Do you make the best decision you can make all the time? As in, are you “right” all the time? Of course you’re not. I know for certain I don’t. But I’ve been getting better, and I know that I’ll keep getting better.
Why? For one thing, because I’m getting older, doing more things, gaining more experience and learning to see more of the possible consequences of my decisions earlier. But, that is not my advice. Heck, it would make for a terrible useless answer to the headline. “Your one step? Get older…”
Decisions, decisions...
No, my advice is simply a case against using your gut feeling. Whenever faced with a decision more complicated than what to have for dinner, consider postponing deciding for about 10 seconds. This should give you time to think through if you’re really sure what you are doing.
Sure, there is such a thing as over thinking, but the 10 seconds should not put you in danger of doing that. 10 days to decide on taking a shower or not will though 
But, taking a little bit extra time to just think through the whole situation will not only open you up for better options that might be just around the corner. If you still, after having thought things through feel like going with your gut decision, you’ll automatically be more confident in the decision.
Will this work all the time? Of course not, don’t be silly. But it allows you to better utilize previous experience and knowledge to make up your mind. Do it, and you’ll see that you automatically get better at making the right call more often.