The increase in shooting percentage is likely a product of higher quality shoots. Better linemates and PP time on the 2nd unit are probably the biggest factors. His most frequent line mates last year were (IIRC) Loui Eriksson (who is a black hole of offense), Brandon Sutter and Markus Granlund. All of these can score in streaks, but none of them really generate offense using their line mates.
This is the first time they have really given him a sustained string of games with top 6 minutes and decent linemates (and remember he started the season playing with Sutter and Schaller). He looks to be a really good fit on Horvat's line - and it gives us a fast, heavy line that is difficult to play against. He played sporadically with the Sedins last year, but they didn't really take advantage of his speed / transition game. He has improved his board work quite a bit, but he was not a good match for the Sedins half court game - and pretty much every time he made the smallest mistake he was back on the bench or on the 4th line.
He has always been very good at controlled zone entries. But when your linemates are a full zone behind you, it leaves you isolated, with few offensive options.
He has also clearly improved his overall thinking of the game at the NHL level. When he got the puck previously, you knew he was going to blast down the wing and try to beat the defense wide. If the defender took the proper angle, it would result in a shot from distance and/or an acute angle or Jake would end up below the goal line or swing behind the net. Those types of rushes tend not to generate high quality shooting opportunities. This year he has made some really nice passes to setup his line mates (he had a gorgeous pass to Horvat the other night). He also at times pulls up to hit a trailing forward or defenseman. More importantly, he is now getting in quick on the forecheck and turning pucks over - resulting in more sustained pressure in the O zone. He is never going to be an assist machine, but if he keeps this up it should result in more assists as well.
PP time also tends to yield better quality shots.