Think of how you learned weak verbs in your native tongue. Then
transfer that over to Biblical Hebrew.
As for me, I just started reading, using an analytical lexicon. After
a few times through Tanakh, my analytical lexicon was falling apart
with pages scattering to the winds, but I had learned most of the
irregular verb forms, including all the most common ones, and a feel
for how to track down the roots for the less common ones, so I no
longer need the analytical lexicon.
This was not a scholarly method and I don't recommend it for class.
But I had studied only two semesters of Biblical Hebrew because I
wanted to read Tanakh, and I was doing that. If you need to learn it
quickly for class, there may be a more appropriate method, but for
simple understanding Tanakh on one's own time, I found this a way to
accomplish my goal without getting frustrated.
To you teachers out there, I can hear you cringing, even through your
keyboards just from your hands touching them.