If you ask for only one thing, I will vote for physical exercise. Our bodies react slowly to change. When you stop physical workout, you don’t realise the loss.Mind relies on a tool called cognitive delusion (we think we know but we really don’t).
Same occurs with exercise. To avoid hard work your mind keeps assuring you that everything is fine and you are intact.The best approach is to take a test.
If you think you can run a mile in 6 minutes that you used to do a year back, try today and you shall be surprised to find out that you simply can’t!
Strength diminishes slowly and we fail to realise the loss unless we really need it. Physical work out is the best investment out there.
A diseased body with a million bucks in your account is of no use.
If you ask for a second best advice, I will recommend automated saving and investing.Third best (actually same as second best) is to avoid loans of any kind.