This is my personal list and opinion of things I wish I knew when I was starting out hence it might help some people:
1. If it sounds too good to be true it is in 95% cases:
When I was starting out I got into facebook ponzis at age of 15 where they'd give out 30-150% ROI per month, usually with some wild ass story "We MaDe SoLaR PaNeLs" and those solar panels bring us 100% ROI and for all your investments we will give you huge ROI... All huge scam, lost bunch of cash when I was starting out with this, made it all back with same kind of sites by just putting cash there for a month then withdrawing it out, this way i make cash before they make their exit scam, was farming them for some time this way and even went into profit.
2. Money makes money
If you find an 20% APY income and you put 1000$ in it you will have only 200$ in 12 months but if you have 300,000$ in it you will have 60,000$ in 12 months from it, that's a simple explanation of money makes more money...
3. Don't pay first
Too many scammers, unless it's someone really really reputable be careful when you're paying first you might lose your money like many on this forum get scammed. If you must do so, at first do in small chunks.
4. Don't aim to make small cash
When i was starting out as 15 i just wanted to make 10$ a day, would barely make 1-2$ a day 6 years ago, when i wanted to start making 200$ a day I at least started making 10-20$, I know it sounds weird but when you think of ways to make 10$ and to make 100$ a day your ideas will be totally diffirent and even if it's a fail, idea that you had in mind to make 100$ daily might reap better results than one you had for making 10$..
5. Practice English
If it's not your native language try to get your English as good as possible, it will open you a world of opportunities
6. Don't overcomplicate/overthink/over prepare things
When i was 16 i made my first anime site, grew an instagram profile for it, didn't want to promote the site until i have first reached 5000 followers, those 5000 might never happen in first place guys, just put your ads from the beginning, i lost thousands of possible visitors by not putting my site out there from beginning, and this is the same for 90% of other stuff, i see people not wanting to put ads on their site untill they reach certain number of visitors lol, just lossing cash.
7. Value time not money
When i was 17 my first manga site blew up to make me 100-200$ daily, at the same time i was working as a freelancer, was spending 3-4 hours daily translating shit for my site to keep making those earnings while i could have paid few 3rd world country freelancers to translate them for me for 5$, would've saved bunch of my time, hiring people, especially cheap labor will always make you progress further, also always tip hefty those who do you good job so that next time they do even better
8. 3rd world country living limitations
Many services like stripe don't accept people in my country, opened my first company in UK at 18 for like 30$, started accepting stripe/other stuff i previously couldn't, if you're someone who's struggling like that, go for 1stformations, open a company in uk and create stripe account, will work like charm in 99% cases.
9. Don't bother and waste time on useless stuff
Ok i had a bad experience with certain hosting i got my refund all is good, like in past I won't go over to their trustpilot to waste 20 minutes on writing a bad review, unless they really really really pissed you off, just don't waste time and move on, and this is just one example of time wasting.. They already have 117 bad reviews yours won't change a thing, they don't give a fuck if they didn't reply to previous ones either.
10. Don't be afraid to try new stuff
i started with ponzi schemes(investing in them as said above), anime sites and fuckin surveys, then it went into referrals for survey sites by creating my site, then from referrals for survey sites from my youtube channel and instagram profiles, then woops i can make more money on instagram and youtube doing other stuff than promoting this shit, then something else and so on, though i have huge addiction onto changing stuff even if it's successful, when i see a method or someone successful at something i just wanna try it out myself regardless if it's good for my current businesses or not, don't be like me there lol...
11. Advertising and finding customers is 90% of work
Customers acquisition, visitors, leads, advertising is 90% of the work and most important one at that, mid product with excellent advertising wins against excellent product with bad/mid advertising. Just make sure your product isn't dogshit though, having a good product will always make your advertisements even stronger!
Anyways those are the things I just though in my head i wish i knew back then, would've probably been more if i thought a bit. Feel free to ask questions.