Pick up a discreet mathematics book. Learn logic, set theory, and writing mathematical proofs (induction, etc.)
I really wish they'd put a class like that right after basic symbolic algebra in normal school curriculum - it's far more useful in the modern world than trigonometry.
I agree whole-heartedly. I work at a large company and I find I can typically formulate business rules in set and function theory in mathematic notation, which typically blows away my peers and associates because they either 1) know it and are impressed to see it used in "business rules" or 2) think it looks like some space-alien language (which it may as well be to them).
Otherwise these rules come out as a set of vague half-instructions that always lead to rounds of revisions in UAT. Oh, and "we only scheduled a week of UAT".
A broader knowledge of discreet theory would be much more helpful than understanding a sine or cosine at a... trigonometric level.
I can't believe no one has mentioned Concrete Mathematics by Knuth & friends yet.
It's incredibly well-written. Very challenging, yet totally approachable and accessible to someone with even just a rather basic (even foggy) understanding of "high-school" math.
I, quite a few times, spent more than four hours with a pencil and paper making my way through 2-4 pages of material, as since my background was lacking, there were parts where I had to figure out how they got from A to B. IIRC, I spent multiple days on a few paragraphs at one point.
That said, it is written how I think math books should be written, is considered part of the start of Discrete Mathematics, and is conversational, illuminating, well-layed-out, and approachable despite it's level of difficulty.
I can't recommend it enough.
Don't view it as something where if you're not making progress you're failing. Take the time to ensure you understand every bit of what you read before moving on, and do all the exercises you can muster.
Can't agree more about the value of Discrete Math. Any programming worth his salt can wax about combinatorics and counting problems at a moment's notice. I'm thoroughly convinced I'd be a few years further along as a programmer had I learned discrete math at an early age.
But anyway, the Teaching Company offers a phenomenal course on Discrete Math, taught by none other than the "Math Magician" Arthur Benjamin (seriously, this guy is magic. He can do 5 digit squares in his head!). It's easily torrent-able / available through more traditional means.
I really wish they'd put a class like that right after basic symbolic algebra in normal school curriculum - it's far more useful in the modern world than trigonometry.