hills, hills and more hills!!

I think it's different for running and biking.

For running, practicing hills will really help you to run hills better. Both the going uphill part, and the recovery at the top.

For biking, you can be a good climber without ever training on a hill. Hills are my strength in biking, but I do almost all my riding on a trainer. It's just a matter of applying power to the pedals. On the other hand, being a good descender requires practice, and to do that you need to see some hills. Practicing your goal course would really help. I'm spending a few weeks in Colorado right now, and my flatland training is serving me fine on the uphill bits, but the locals make a mockery of me on the downhill bits.

I'm lucky enough to live in a very hilly area  - ridiculous rollers on one side of town, and actual mountain climbs on the other. So I just run and ride. For runs, I frequently make them into hill "intervals" (I use that term liberally) meaning I'll run at just under race pace on the incline and run easy on the declines. I concentrate a lot on my form running uphills - if I think of driving my elbows toward the ground, it forces me to engage my core more, and while not scientific in the least, it seems to work for me.

On the bike, I try to climb with a group of stronger riders as often as possible, and play with shifting and acceleration to teach myself to better attack rollers while maintaining speed up and over the crest of the hill. I do not use a computer of any sorts, and (for road cycling at least) riding based on feel, rhythm, and a stubborn refusal to dwell on how "hard" a climb is seems to work for me.

All this said, I am a bit unorthodox for a triathlete and about as un-type-A as a dedicated, competitive triathlete can get.

Good luck - hills are fun