I am currently away from EVE for two weeks. December will be a low month in trade profits as a result, but in November I hit 20b in profit for the first time:
My play time did not increase, but my profits did. There are a few explanations for this:
1. In late October I reviewed all of my orders, threw out those items (around 20b isk in stock) that were not making decent isk but also needed to be updated frequently. I only trade in competitive items when I can be sure some will usually sell before I get out bid, otherwise I stick with low competition goods that sell just enough to be worthwhile. In total, I changed around 40% of my stock, and it looks like it paid off.
2. November had some of the highest activity in EVE in 2014. New and returning players in particular mean more market activity.
3. Moving large goods has become increasingly unattractive in late 2014. Ever since Red Frog started charging more for shipping, both because of slowly warp times and, later, because of CODE. freighter ganking, I've seen less competition for large goods. Since I do my own shipping, and have not (yet) lost a hauler, this is great news for me.
Investments in November: In November and early December I used some liquid isk to made a few investments and experiments. First, I stocked up on some of the items I sell that are selling at 3+ month lows, which has already started to pay off. Second, I bought materials for some bowheads. Third, just for fun, I bought a virtue set for a "perfect" scanner.
Fourth, though, I tried my hand at some market manipulation, just to see what would happen. I carefully (I thought) picked an item in Jita that was (apparently) under-priced and would (apparently) be hard to quickly re-stock. I cleared out the sell orders and started re-listing the items. Other players had stock as well it seemed, and, instead of riding the wave, just listed the prices at 5-10% of the original value, which I thought was strange. In total, I spent maybe 3b isk and only made a profit of around 200-300m. Not bad, but not worth the time. Maybe I will have better luck in the future.
20 billion in a single month is an important milestone.
Regarding your market manipulation attempt, a lot of times, especially in high volume, well supplied markets it's best to just sell for 5-10% more than the usual price whenever you can. If you try to "ride the wave" about all that happens is the no-lifers and bots undercut you constantly, your stuff doesn't sell and you wind up selling for even less in the end.
On the other hand if someone tried to jack the price up 100% and you list at only 10% over the usual price they often won't undercut you at all and your stuff sells for 10% more than usual. In a long term strategy that's when you sell, when someone else tries to manipulate the market way up.