You might forget about it since it is not within your eyesight on a regular basis, but you have to remember that you’re still spending a lot of time in your bedroom, so the dirt, dust, and gunk will accumulate underneath your bed whether you see it or not.
You don’t have to vacuum under your bed every time you vacuum, however it is important to try to do this at least twice a month because you don’t want to be breathing in any of this unsanitary air. This is especially true if this gunk accumulates over a prolonged amount of time.
You can make this a part of your routine. If you can’t manage to get to it twice a month, try at the very least to do it at least once a month. Of course, the more you clean under the bed, the cleaner your air will be.
To properly clean under your bed, clear out any items that you might be storing there and then begin sweeping or vacuuming. If you want to automate this process and make it easier for yourself, you can use a robot vacuum cleaner.
If you find that dust bunnies are evading you, you can use a hair dryer to move them around and more easily vacuum them up.