I look after a couple of tenebrio molitor cultures, it's very easy. A couple of inches of bran will keep them going for months, if you keep them at just above room temperature they'll breed like crazy. The colonies are virtually indestructible in terms of feeding, you can leave them for months without touching them and they'll be fine.
I clean out the tanks a few times a year - I use a spoon and tip everything into a sieve. The beetles and mealworms stay on the top, whereas the chewed-up bran goes to the bottom, it makes great compost. I occasionally chop up an apple to put in or wet a slice of bread, but one thing you need to be careful of is not to put in any cooked potato. I did this once and within a few days the tank was covered in a horrible fungus.
If you're worried about whether there's enough food, check for any dead pupae or any bits of beetles (e.g. heads). These are signs that the adult beetles are eating the pupae or each other and therefore that they're running low on food. Another sign is a distinct lack of adults, but an abundance of mealworms (showing that the eggs are being laid, but few larvae are making it to adulthood).
I hope this is helpful - the larvae are great as a food source and they also display complete metamorphosis.