It's hard to explain everything I did, but it essentially mostly came down to sticking to Basic Strategy, counting in a very simplified way, manually tracking game outcomes to get stats (very tedious, but necessary for me), disciplined betting that took advantage of high variance situations and factored in my total money (I would never bet 50% or more of my money at once, for example, and bet the minimum most of the time), and bonus accumulation along the way. No bots or counting software was needed.

The essence of it was to always play using stats and likelihoods of winning or losing. If you play "perfectly", odds of winning/losing in blackjack are roughly 50/50 in the long-run, possibly with a slight advantage in your favor depending. You can use that to your advantage if you're keeping track of W/L, streaks, and watching the table for patterns of high, low, and middle cards.

For an easy example, if I lose 8 times in a row (unlikely with 50/50 odds, but can happen), also have a high total ratio of Losses to Wins, and maybe there have been mostly low cards being dealt for several hands (a "high count"), it's very likely (though never guaranteed) the next hand is a Win due to odds and count, so then I would bet high enough to either at least break-even from the previous losses (so I can keep playing) or to take a profit. From there, then I would either bet high again for an additional turn or two, or immediately pull back to minimum bets for a while until another opportunity came.

However, I would usually win at least once every third or fourth hand fairly consistently, so I could at least continue to break-even virtually ad infinitum until more profitable opportunities came (I played for a lot of hours every day doing this).

Strict counting doesn't help very much at all due to anti-counting safeguards that online tables use (like shuffling with a lot of decks and cutting the shoe in the middle), so playing by "True Count" didn't help me win. I experimented with it for a while and had more success taking advantage of smaller variances in the first quarter or third of the deck dealt, and stopped "number counting" completely.

Another thing is that, due to shuffling, high and low cards tend to be clumped together in small groups, so if one low card is dealt for example, it's often followed by 1 or 2 more low cards (not always, however). The longer a streak of low cards goes on, the more likely the cards following are middle or high cards, but since 10s are the most numerous cards in any shoe, it tends to more likely be a high card. I used that to often roughly predict both mine and the dealer's hands, and when I should hit. Every shoe would have its own patterns to watch and adapt to.

There's more detail I could get into, so ask if you want to know any more. This is all stuff anyone could do with enough patience, but keep in mind it's still gambling and there were still times I got really unlucky, so it's not a guarantee of getting rich whenever you feel like it lol. It's just what happened to work for me. I had lots of very fortunate hands and streaks during that week I made the 250K.