As technical as the sport of swimming can be, it is tough to narrow down the answer to the often-asked question, "what should I concentrate on?"
Improving your core strength is just a small way to vastly increase your capacity to crush the bike course.
Running after riding a bike is different from running on fresh legs. A hard bike ride makes you feel heavy-legged and uncoordinated when you start running. Nobody runs as fast after a hard bike ride as he or she does in a standalone run.