Have you ever tried to explain the present perfect tense?
The present perfect is a common tense in English, but it is one of the tougher ones to learn. First of all, there are two distinct uses. Second of all, one use is similar to the simple past, and the other is very similar to the present perfect progressive (also known as the present perfect continuous).
What's the best way to present and explain all this to your students? For lower‑level learners, present the two uses on different days. For higher‑level learners, present the two uses at the same time so that they realize why they hear the present perfect used in different contexts. And, of course, give them plenty of examples and practice!
For a direct comparison of these two tenses, see the chart and examples in this post: Present Perfect Vs. Present Perfect Progressive
Overall, your students should be able to easily remember Use #1 by thinking of the "when/no when" rule (when = simple past, no when = present perfect). Use #2 is easy when you teach the present perfect alone, but trickier when you compare it with the present perfect progressive. This post, Present Perfect Vs. Present Perfect Progressive, has charts and tips comparing these two tenses.
Make sure you reinforce that the present perfect (have + p.p.) can be used for a continuing action, not just a completed past action. Students often have trouble remembering this since all other continuous tenses in English use an ‑ing verb. Also, some textbooks only focus on Use #1 and don't mention the continuing meaning of the present perfect, but it is very common and should be taught.
Note that as a time marker, still has two meanings and uses, so be careful that your students don't get confused. Still can be used with the present perfect for a finished past action (as in Use #1, above), but it can also be used with the present progressive to emphasize an ongoing action, as in I am still waiting for your call. Students can easily keep these tenses straight by noticing the different sentence patterns (still + have + not + p.p. for the present perfect and be + still + ‑ing verb for the present progressive).