I too find the notion of direction very confusing. I'd rather think of what is described as multidirectionalness as a property or a capability. Only the "multidirectional" member of each pair of verbs of motion can be used with I can - я умею (or, more generally, to be able to - уметь). The logic then goes like this: I can do it => I tend to do it sometimes (habitually) => this motion tends to occur in various ways (and directions). Hence:
Сова умеет летать => сова летает => сова летает бесшумно
(The owl can fly => the owl flies => the owl flies quietly - indefinite tense)
As opposed to a motion which is happening here and now:
Сова летит на север (The owl is flying North - continuous tense)
Unfortunately there are situations where this notion of property/capability/habit does not help:
Сова летает над полем (туда-сюда) - the owl is flying over the field (back and fro)
Although Russian uses летать here, English still calls for Present Continuous because the motion is happening here and now. In such situations multidirectionalness seems to be your only guide. I would suggest to first think if the motion is described in English using a continuous tense. If the answer is yes then think if the motion is occurring in multiple directions. If the answer is still yes then you most certainly need the multidirectional (habitual) member of the verb pair.
And to make matters worse:
Now or habitually? - Habitually. (Multidirectional verb then? - No, wait for it)
Does the sentence explicitly mention a single direction or route? - Yes!
You need the unidirectional verb.
Зимой птицы летят на юг - In winter birds fly South.