Verb aspect in Russian is very confusing for the foreigners. Looks like formal rules don't work good in this case while native speakers use it completely intuitively.

Usually one can replace any verb with its aspect couple and get a correct new sentence but with a different (sometimes bizarre) meaning. So my current strategy to explain for the foreigners the aspect is to avoid formal generalization but to translate an example sentence two times with different aspect and thus show the difference to help with intuitive understanding. That's what I came to after many explanations.

я хочу приезжать - I'd like to come sometimes.
я хочу приехать - I want to come (right now).

ты не можешь слушать – you are unable to listen (you are deaf)
ты не можешь послушать - you can't listen (what I am talking to you because you go away right now)

я должен работать - I must be working (otherwise they will call me lazy bones).
я должен поработать - I must do some work (then we'll have fun).

я стараюсь понимать – (Usually) I try to understand (their way of thinking)
я стараюсь понять - I am trying to understand (what you told me last time)