Habits reflect the kind of person you are. Not many realize the power of simple habits that if followed regularly can benefit you manifold than the effort you put in.
My three mini habits
1. Brush your teeth twice daily, if possible floss too - I never realized that this pretty simple habit can have so much potential benefit. Brushing and flossing your teeth properly prevents gingivitis and periodontitis which supposedly affects our health seriously during old age. You can find numerous research article titled, 'Why brushing twice daily increases your life expectancy?' For anyone feeling embarrassed now, it's ok! You are never too late to start something good. Before sleeping, brush your teeth properly (gently, and in a circular motion. Clean your tongue too) and use floss to clean the gaps between teeth. Don't feel lazy to spare just 3 min, it increases your life! (even if you are ignorant just do it)
2. Look at the dark ceiling before sleeping - This habit is no different than what other people have mentioned as introspect. But I'm mentioning it in concrete terms because many people don't know how and when to introspect. This simple trick works fine for me because I can't find time otherwise. Looking at the dark ceiling reflect on what you did today, ask yourself "If you were busy or productive today!" Why is this question so important? Normally all the problems whether it's health, work, study, play, relationships, are all dependent on how best you manage your time (see 3rd habit). So without realizing how well you managed your today, you would probably end up squandering away your precious time tomorrow being busy and not productive. Read my answer on I'm a twenty-something. What should be my top priority? to why daily improvement should be your only priority when you are a twenty-something.
3. Plan your tomorrow, today - This is no new knowledge. Almost all the productivity content you would read on the internet talks about planning your day ahead. I can understand that planning a Sunday on your calendar may sound crap to some people. But, believe me this habit will benefit you in the long run.
Managing time is an art and only a few people know how to do it. And, a majority of those who do it exercise a better control on their lives. You feel empowered and confident when you know in advance what to do today?
I'm an engineer and a happy one. My work timings are usual 9 - 5PM, which makes it 8 hours of which I actually work for 3-5 hours with utmost productivity. The 90/10 percent rule rules everywhere. A day ahead or while commuting to the office I divide my today's work into the 90/10 figure. What that means is I'm able to finish 90% of my work during the most productive hours which are usually 11 - 1PM or 3 - 430PM. Hence, leaving enough room to pursue whatever I like and be stress-free.
So, brush twice, introspect while looking at the ceiling, and plan your tomorrow ahead!