I don't believe there's anything in life you can't go back and fix. The ancient Vedas - the oldest Hindu philosophy - and modern science agree that time is an illusion. If that's true, there's no such thing as a past or a future - it's all one huge now. So what you fix now affects the past and the future.
Five Great Habits for Better Relationships: acceptance (smile each time), appreciation (say thank you to everyone), admiration (compliment people on their appearance or clothing, etc. ), approval (praise immediately, specifically and repeatedly), and attention (be a good listener).