What to work on? As I've often advised my kids (and anybody else polite enough to listen), you should always take on the most severe challenges that you can handle. If feasible try to find something that's tough for you but even tougher for other folks. In any event don't go for areas with low barriers to entry. So will everybody else; the resulting competition will kill you and reduce the ultimate payoff. The world is full of video gamers and garage bands (and blogs, and advice on self-improvement, eh?!).
I was amused recently to encounter a comment by Samuel Johnson on the topic of music --- specifically the violin, a notoriously hard instrument --- that lined up with my notions of comparative advantage. From Boswell's Life of Johnson, a fragment of a conversation held on 15 April 1773:
GOLDSMITH: "The greatest musical performers have but small emoluments. Giardini, I am told, does not get above seven hundred a year."
JOHNSON: "That is indeed but little for a man to get, who does best that which so many endeavour to do. There is nothing, I think, in which the power of art is shown so much as in playing on the fiddle. In all other things we can do something at first. Any man will forge a bar of iron, if you give him a hammer; not so well as a smith, but tolerably. A man will saw a piece of wood, and make a box, though a clumsy one; but give him a fiddle and a fiddle-stick, and he can do nothing."
If you invest the time and effort to climb a steep learning curve, eventually you can do extraordinary things. And even if monetary rewards are small, there's tremendous psychic profit from doing the difficult well ...
(see also ShotgunsAndRifles (6 Nov 1999), ZhurnalAnniversary2 (4 Apr 2001), AdvantEdge (15 Apr 2001), TenThousandHours (20 Sep 2001), SelfStandardization (6 Apr 2002), MyOb (18 Aug 2002), MillenniumMath (5 Dec 2002), ...)