Brick sessions. Go out on your bike for a normal distance training ride, put it in the house/garage etc and then go straight out for a run. Only way realistically of adapting to the feeling of going from using one group of muscles to another.
You'll naturally be tired anyway having done the swim first followed by the cycling.
A couple of other things to be aware of are using your legs to much when swimming as well and using a gear to high on the bike as I find this fatigues your upper legs quite a bit. A higher cadence on your bike (harder in terms of aerobic management) could help with tired legs and give you a better start on your run.
How do you feel your training went last year?
And good luck of course.