To be determined to have a happy day always keep a smile on your face and in your mind. Here's how.....
If something bad happens to you that would mess with your oh so important 'to do list' that is probably ever growing, forget about your today's thing to do list and do it tomorrow.
To help you feel comfortable about you doing this, write your present moment thoughts and feelings down, so you know you can look after your mind at a point of your life that has more free time. This will prove to you that you are wise beyond your years.
If you have to do something to do with your finances, home or your job, because there is something that would affect your personal life (career or finances crumbling are never good for one hey) - ask a close friend if they can do it or them for you - tell them you'd do the same for them if they needed you to help them out.
If you annoyingly lose a possession that at first glance is rather special to you - briefly try to look for it, but don't emotionally exhaust yourself by searching for it too much. If you have a good look for it , but you can't find it - it obviously wasn't meant to be part of your life.
If it's an item of clothing - you could treat yourself to a new one - I bet you'll still look fab in your new clothing item(s). If you can't afford a replacement, try asking a close friend if they could lend you enough money, or if they have something similar, ask if you could borrow it for a while or have it. If they really care about you, I bet they'll help you out.
Let yourself feel it in your mind and body that you're content and happy - your system (your: body and mind) will obey your good old brain when you say "I am happy because I'm healthy, loved by my family & friends and I'm happy with the way my life is going along so well - so I have an internally chuffed feeling - GO ME!".