super vague question but here we go
i don't know 100% how to do that but i get some of the theory at least.
lets start with your diet. GIGO (garbage in, garbage out). so you should remember the food pyramid:
Food Pyramid for a healthy, nutritious and varied diet for 1-5 year old children from Park Academy’s Chef Rohan. A guide for what should and should not be included in your child's diet.
www.parkchildcare.ie
7 handfuls of fruit/veg.
5 handfuls of rice or bread or even oats.
pint of milk or a yogurt or something.
a fish or a piece of chicken, pork, beef etc. (vegetarian or vegan equivalent if necessary)
oils (ideally good oils).
a cookie or 2.
now i wont pretend to do any of this because i eat like a savage, but, it can easily be done:
wake up, brush teeth, drink glass of water, make bed,
for breakfast we have oats in milk (porridge) topped with a handful of berries, finished off with an actimel or yogurt. this has 2 or 3 handfuls of grain type stuff which gives slow release energy, the milky goodness we all crave plus some bacteria that's good for your tummy and bones AND you've done 1/7 of your fruit and veg which gives fast energy.
next we have lunch. its still kind of early in your day so you don't want anything too heavy. a sandwich will do the trick. bacon lettuce tomato or maybe tuna sweetcorn. as long as you get a handful of veg and a little meat you'll be fine for a couple more hours. sandwich ticks off cereals, more veg and meat which is usually high in protein and iron. through your day, you'll use muscle, they'll get damaged and will need to be repaired. this is what protein is for. iron is good for blood.
onigiri (riceball) is another good option.
after lunch is dinner, your main meal. the hard part of your day is over so you wont need grains so much but you have alot of fruit and veg to eat plus you want good oils. fish and olives have good oils. maybe a steamed fish on a nice salad and a small side of rice? omega 3 from fish is good for your brain, the salad has all kinds of stuff going for it. remember that plants come from the floor and the floor has minerals that you need. plants also usually have vitamin c which you need to fight off the flu.
so supper is last. something light because you want to sleep soon. soup is good. its warm, fast to make, eat and its made of vegetables. its been a long day and you should reward yourself for making it through another day and holding it together. you've earned a cookie. go you

brush your teeth, glass of water and go to bed.
might be worth noting that we all like snacks. carrots and grapes are good snacks.
after your diet comes your MIND. this ones tricky because you cant rewrite your brain as easily as you change your diet. having a healthy diet is a good place to start when taking psychological care of yourself because you now have access to vitamins, minerals, oils and your brain can make all kinds of chemicals. honestly, happiness is objective. just like how good and evil looks different to everyone. i don't know what happiness looks like to you but some stuff is universal across people i think so ill throw some suggestions out there.
take up martial arts. this builds confidence. if you had no confidence, you wouldn't take a step forward because you'd worry that you wouldn't reach the end goal. why take the first step of a marathon if you don't think you'll even finish, right? wrong. every step forward is progress even if you don't reach the end.
make lemonade. life only knows how to give you lemons and it wont stop until you're dead. making lemonade isn't about being optimistic per se, its about making the best out of a bad situation. say someone hands you a block of ice for no reason...well what are you gonna do with that? its ice and you're not hot so you don't want it...but you ARE thirsty. maybe right now its ice, but later it'll be a glass of water
touch grass. concrete, glass, phones, planes, sirens etc etc etc being a human is stressful and tiring. take regular breaks from the stress and the noise and just meditate or take a nap in the middle of nowhere. i have 2 spots i go to: one up high to put things back into scale, and one spot far away from everything where the only things breaking the silence is planes and birds. being in nature does wonders for your morale.
that's all the typing i can do for now.
hope this helps.