I'd throw myself into correspondence / online education to get better grades much quicker than I did. I dropped out at 19 with 8 credits to go. Not because I'm unable to perform well academically. My grades before and after high-school say otherwise. The pursuits and accomplishments I've managed in a highly academic field with harm reduction and drug policy in my 30s suggest that especially.
But I had some temperamental issues with undiagnosed issues of PTSD, bipolar depression, anhedonia to bright and humorous, and social anxiety to stigma preventing me (at the time) from being able to express myself. I have a autism spectrum disorder as well which wasn't diagnosed until my mid 20s.
When I was 14 and 15 I had serious issues with issues with conflict with my family members at home, soft to hard drug use, a pre-alcoholism running wild, and not being able to understand who and where I was in life. I was angry and sad to the point I could barely move. People treated me like shit truly so I rebelled and by the time I was 16...
When I was 16 things did calm down and I went back to school after dropping 3 / 4 semesters I was supposed to be in school for at that time. In grade 11 I was still technically halfway through grade 9. I did finally start to come out of my shell and attend most of my classes regularly enough to pass.
But the damage was already done and my efforts were never to the point that they caught me up. I would've been in high school until I was 20 if I stayed.
I wrote my GED instead at 20 and I scored scores like 97th percentile in math, 92nd and 87th on English reading comprehension and in writing. The other two scores were in the 80s in percentile somewhere.
My paper said I scored in the top 10 percent comparatively with their group of graduating grade 12 students who wrote the same test.I was happy with that at the time, but no one thinks a GED is that great. No one asks what your results were or even really knows that you do get grades like this on a GED. A diploma is key, in a social context, and oftentimes a degree and a shit ton of experience somehow. Even if it's your first job in a field.
When I was 16, I didn't know all of this. Since a year or two after getting my GED I've always lied about it and said I got my OSSD. No one checks. I've gained some college grades and a shit ton of experience to overcome my high school years anyway. I've learned how networking and being socially on par with an employer and a good interview means more than your piece of paper. So does your actual honest to God chops and knowledge going in.
If you've never been in a job type, or a whole field before - you need to make doubly sure you've researched the hell out of a company prior to interview. Preferably through their documents which should online with a site:their site) AND filetype: pdf or something similar.
site:xxxfactory.biz AND filetype:doc employee handjobbook
is an example of "dorking" a search engine for this kind of material.

THEN learn the introductory material to the field, and anything which screams important by the particular company to a superficial level. I say superficial because interviews are superficial and introductory as in you're not deep into the work yet. An interviewee is a sales position and it needs to get treated as such. Do NOT be afraid to sell yourself or to negotiate!
Anyway, sermon is over.
If I could go back to 16, I would take my education more seriously and I would have done as much of it through correspondence and online education as possible. I would do less drugs and drinking and more of the actual social involvement and music / drama / writing geek stuff I was into.
I played a lot of music and performed in a lot of assemblies in high school. I loved the creative arts. I had ideals and I had the gumption for some debate club style social strategy and volunteerism to making change.
I wish I could have just followed my dreams and been someone who writes and works on a social activists level much earlier. I wish I spent more time on music and made the bands which I did start more of a reality. I wish I figured out my actual diagnoses much earlier.
I wish the engagement in harm reduction materials and forums similar to Bluelight actually led me to learn what harm reduction is too. For whatever reason, I didn't the term and philosophy of it until I was 29 and 30 respectively.
sidenote: I wish Bluelight had "harm reduction" in the banner because I did know about and occasionally browse this site at the time. Dead serious, I've been miffed at the realization of how dire the SEO and lack of banner level harm reduction is to this site. It's the absolute main reason traffic is down way more than Google changing any algorithm in 2018. Forums are not suppressed, nor harm reduction related material. Bluelight didn't keep up with the evolving standards of an indexed web, or run through the tooling and SEO and analytics stuff which Google set out throughly, or use any of its donation money to buy keywords or design a greater banner plus hire an SEO professional. I could bang my head on the wall knowing all of this in detail and also seeing the glaring and easy to fix in a day or a week scripting issues.
Honestly my final answer to this is I wish that I knew how important this drug users activism actually is to me, the world, and harm reduction, everything. I would've been much more accomplished in all of this by now if I understood how much value this sort of thing has in my life.
But no one showed me and I didn't manage to teach myself. I didn't known to the level I do now how to educate myself and participate on a world stage at any level. The tools in 2007 for this were almost the same as they are now. I fell behind for ignorance and a lack of nurturance.
Nurturance is a big deal to kids 16 years old. I felt dead alone.