Oh wow... where to start! 
When I was young, I paid the minimum monthly payment on many of my cards, and I even knew just how far I could run them up before the payment changed. I practically 'accepted' that I would always have a payment - it was simply worked into my budget, without any consideration to the amount of interest I was paying (which was considerable).
Now, instead of me paying monthly interest, I PIF and the cards pay me monthly in cash rewards. I currently earn around $50 each month in cash rewards, which while not Earth-shattering it a far cry from paying hundreds a month in interest! Actually, the thought of paying even a few dollars in interest is so unsavory I'll go to great lengths not to do so (sometimes nearly to the point of being absurd, but it works for me).
During my recent rebuild I didn't know what 'gardening' was, but I was doing so unintentionally. Had I known then what I know now, I would have started trying to get new credit much earlier than I did. I erroneously thought that I didn't have any chances of getting credit, so I simply didn't try. Had I started earlier, it would have made my "come back" quite a bit faster.
If I knew then what I know now...
1) I would have got credit a lot sooner. Instead I had to fight against the "credit is bad" mentality I was raised with and still surrounded with. They all told me if I got a credit card I would sink myself into a hole of debt. I proved them wrong. But it would have been a whole lot easier to prove them wrong if I hadn't waited until I direly needed credit before getting it. As it stands, my oldest card is still under 2yrs.
2) I would have requested a much higher starting limit. $750 is really quite low, as it turns out. 
3) I would have apped more carefully. I had no concept of what a hard pull was, or the fact that just becuase I had a credit card didn't necessarily mean I had a credit score yet. I couldn't understand why I was being turned down for having no credit score, and why I was turned down for a CLI when I needed it (three tires blown in two months, plus 4 major emergency mechanical repairs...last winter was stupid rough).
4) I would have actually watched my utilization. I didn't realize it mattered! I thought that as long as I paid it off they would have no reason to care. I was constantly at 90+% UTI. I only ever paid interest twice, and kept on top of my finances, but not in a way that paid any attention to UTI. Once I began watching that my score shot up brilliantly from the low 600's to the 700's over the course of like 2 months.
5) I would have used bank loans rather than undocumented personal loans.
I am SO freakin' relieved to be on the right track, and it's all thanks to the smart folks here willing to share their knowledge and experiences. 
After a lot of research I apped smartly for one card and got it with a 15K SL, and the bonuses and 0% APR helped me save money in other ways. Which means now within a couple months or so I'll have saved up enough to take out a savings secured loan so that I have more of a mix than just the three credit cards, and then it'll be garden time.
I cannot begin to describe how good it feels to be so on top of things. As I've mentioned elsewhere, I'm homeless and live off of $733/month income. Seeing my score increase now through the 700's is a way of proving to myself that I'm doing a damn fine job of making life work. I love it!!
@live-n-learn wrote:
@Anonymous,
Your #5) I would have used bank loans rather than undocumented personal loans.
can you elaborate???
I've now had three loans that never reported, because they were all done informally, just friends/family loaning me money to get me out of a jam. The awesome thing about this is that they are easygoing about paying it back and aren't charging me interest. The less-than-awesome thing about it is as far as FICO is concerned I have zero history with loans.
In my particular situation, I suffered severe neurological disability for several years that rendered me incapable of handling any finances, so that task was delegated to my primary caregiver, who so happened to be my mother. Without my knowledge she overspent by compensating with her money under the assumption I would pay them back, so that when my health recovered enough to manage my own finances again I was told I was over $2,000 in debt to my parents.
The living situation with my parents went sideways when they had to adjust to me being capable of thinking for myself, worsening to the point that escape became imperative, even though I was still too disabled to work and couldn't afford to live elsewhere. Three friends of mine pooled together to loan me $5K, which I used to purchase a van, deck it out with some living essentials (e.g. fridge), and repay my parents right before jetting off to start a new life for myself on the streets--struggling, but free.
I'm not getting any love from FICO on any of these loans, because aside from a note in Social Security's records there's no documentation that the loans actually exist(ed). So now while I work on obtaining a credit-building installment loan, I'm simultaneously planning out how to pay back the 5K loans and just wishing I was getting some credit (heh) for doing so.