
I'm human. Due to health issues in 2011, I couldn't keep on top of everything and trashed my cleaned up credit. Thankfully, it was only a partial slip, but I feel stupid that I'm back to where I was in 2007 after having cleaned everything up. Fortunately, I'm not back to where I was in 2004, so I suppose I should be thankful for that.
Here's my current status:

Since August, 2004, I've made a concerted effort to clean up my rather-trashed credit, which had been at least moderately good up until my husband died. While he died more than seven years ago, some of the financial effects did not occur until several years later, when the house of cards finally came tumbling down.

The + numbers beneath each score show how many points I've increased my FICO score for that credit reporting agency. The "Classic Risk" FICO score ranges from 300-850 points, so there's a 550-point range overall. In other words, 100 points is a lot.
When I first pulled my credit reports in 2004, I remember exactly where I was sitting: in a hotel in Boston. I was, to put it mildly, horrified. I knew my credit would be bad, but there were so many names I didn't recognize on my report. I was desolate. I'd recently been turned down for a credit card from a deep subprime lender. Searching on that lender's name on Google, I came across Art of Credit (sadly no longer), Credit Info Center and, later Credit Boards. I've also been active on Infinite Credit. Of all of these boards, Credit Boards is the largest and most diverse.
I learned a lot about what I needed to do to tackle the problem, and wrote myself a short list for each month. I didn't want to tackle everything all at once.
There's been various threads on both boards about how one keeps organized. I use charts. For example, this is one of my motivating charts:

As you can see, I had 35 negative items on my combined credit reports when I started, consisting of:
Not every credit reporting agency has the same negative items. Here's the view over time:

Let's contrast that with the current revolving credit I had at the time:
I've now closed all of my rebuilder accounts.
Currently I have:
Lots more quantity, some improvement in quality, but I'm Not There Yet.
As time progressed, I had fewer "baddies" - some of the accounts really weren't mine. In fact, I found out about a case of identity theft as a result of this process, where someone had opened up a cell phone account in my name, then stopped paying for it. It had been hurting me for years, but I'd never known. I've gone from seventeen total positive accounts to forty-two, almost all of which were new tradelines.
In a couple of cases, the negatives were so old that they stopped hurting me. Some of my late payments "fell off" my report, making a negative tradeline into a positive one. In short, it took over 100 certified mail letters (all return receipt requested, of course) to get the kind of change I did. I had to keep track of everything. It was a lot of work.
There's no one answer, and I'm not just saying that. Here's a graph of my FICO progress over time:

Much of the initial gain is due to the aging of the extremely recent lates, I suspect. In other words, I first checked when I was in a trough.
But, getting back to time, here's some upcoming milestones for me:
I really only worked at this hard for about 8 months, then took about 8 months off when I did nothing credit-wise, and come back to it every now and again.
What's currently hurting my credit the most (other than things time will heal) is high utilization. I estimate that I may be able to get another 100 points if I pay off the remaining chargeoff (around $500) and get my total utilization down to under 25%. (For those of you who don't know the term, utilization is the relative percentage of how much you're using on your credit cards compared to the credit limits. Currently, I'm using nearly 70%, which is awful. But, like I said, I have this new job....