Yes, I agree that students find it difficult to understand the present perfect tense. The technique I use is...comparing the present perfect and past simple tense. Past simple tense is used when the time is specified, whereas Present perfect is used when the time is not specified.

I have met John.

I met John last week.

I kowning the different presents is not as import as learning. You student will learn over time the differences but it takes time. Just teach and don't spent time on identifying what something is unless it is a student want or desire.

You can compare with your student some similar sentences:

Every year I buy a new shirt (a regular action - Present Simple)

I'm buying a new shirt at the moment. (a process - Present Continuous)

I've bought a new shirt (a result without giving the time - Present Perfect)

Yesterday I bough a new shirt (the action in the past - Past Simple)

Some visual clues that go with example sentences. Create a presentation named "Present perfect" in Powerpoint. Visual clues really help with what you are trying to explain.