The first criteria is availability of either pollen or nectar.
Then it's genetic. Most worker bees are either pollen collectors or nectar collectors, a few do both, but by and large they specialise in one or the other. This means you can breed queens that produce high pollen collectors or high nectar collectors.
Then there are the switches inside the hive for pollen collection, if plenty of pollen the pollen collectors don't (usually) go and collect more.
Not sure what I've got as they are honey monsters who also collect excess pollen. If someone could devise a fool proof way of removing stored pollen from brood frames I'd invest in them.