A shounen anime's target audiences are teen/young males. Now that definitions are out of the way, here's how to make your typical shounen anime.
THE MAIN CHARACTER
Time to play “spot the main character”. This game's record is one second because you'll notice him due to his nearly-obligatory unique hair. Have you seen Yu-Gi-Oh? There's a chance that you'll ask the words “What's you-gee-oh?”, but the minute I show you a picture of Yami Yugi, you'll immediately recognise him as that one dude who battles with those weird monsters that pop out of absolutely normal trading cards. Hands down, if he ain't got cool, anime hair, he ain't a real anime hero.
After the bankruptcy of the local parlour, your next job is to make your MC absolutely GGWP overpowered. This needs to be handled carefully though, because he must work for all his powers. Layer this with the fact that the MC also tends to have some sort of hidden power which makes him about a million times stronger. A final layer you can add is that these hidden powers are very dark and mysterious and it'll be a burden rather than a help for a long time before MC finally learns how to control it.
Honestly, building the MC is a lot of work because he often has to have the coolest hair and the coolest powers, but the good news is that his traits are much simpler to craft. He's a fiery-tempered, overexcited, confidently insecure, cool-headed, smart, dumb, friendly, rude, hard-working, lazy dude, who is a hard-core idealist fighting against the cynicism of the world and the Main Villain, and is probably the “Chosen One”. See? Easy. You just have to juggle the traits depending on the situation, that's all.
Now, off to the next point, because I can practically hear the creator of One-Punch Man laughing his socks off at me for this portion of the article.
THE MAIN VILLAIN
Create MC's initially-more-powerful polar opposite. There, done.
THE SUPPORTING CAST
The relevance of the supporting cast depends on two things -- their numbers and how much you care to develop them. They consist of:
a. The romantic interests. Despite all the shipping, it's obvious who the MC will end up with.
b. The best-buddy second fiddles. Typically you'll have the forever-alone comic relief, who gets a nosebleed for each female who walks by; the 24/7 brooding dude; the rival dude, who is there to challenge the MC and will be one of the main people in helping discover/improve his powers; the non-romantic interest females; and the actual smart guy who the group would probably dead without. Sometimes, the different types of second fiddles are packed into one or two people.
c. The partially overpowered mentor who helps the MC to surpass him/her to become GGWP overpowered.
d. Every other expendable character whose names you might actually remember because the anime is 500 episodes long (with 200 filler episodes).
e. The expendable villains who are only there so our MC can get powerful enough to face the MV.
Alas! Our MC has such a tragic past where his parents are dead, or abusive, or have abandoned him, or *error 404: parents literally not found*. Simply put: it's related to his parents. This causes him to start off weak and powerless, with few or no friends. Through a twist of fate, followed by determined work, he gradually begins to move beyond this position and finds powers, friends, fame, love, etc. Of course, all his powers only come after all the turmoil he faces throughout his life and internal monologues during or after a battle. He keeps breaking his limits every story arc until he's so strong he can 720 no scope pretty much every villain he faces and get them 110% rekt. Just remember though, he has to at least fail once against every villain except the very first villain, who later becomes the butt of many jokes, or forgotten.
The supporting cast grows with our MC but frankly, they're there to remind us how ridiculously overpowered our hero is, and that no matter how hopeless the battle, all you need to do is to have your homeboy give a loud speech mid-battle (which the villains will patiently listen to, for some reason) about the power of friendship, and suddenly everyone gets a power boost and the villain is defeated. One of the second fiddles may also die at some point, thereby giving the MC a massive power boost that will help him win the fight. A power boost may also arrive after a flashback to some important moment in the characters' past that's related to the battle.
Finally, after all these shenanigans, MC and his gang triumph against all odds and everyone lives happily ever after. The end… that is, until the next arc where you rinse and repeat everything.
And there you have it, everything you need to make a shounen anime. Enjoy.
Rasheed Khan is a hug monster making good music but terrible puns and jokes where he's probably the only one laughing. Ask him how to pronounce his name at firstname.lastname@example.org