When you see lām before an imperfect verb, decide in this order:
1. Read the whole sentence: does it mean “so that” or “should/let”?
2. In the first ending group, inspect the ending: fatḥah points to Lam Kay; sukun points to Lam al-Amr.
3. In the second and third groups, rely on context when the surface form is identical.
4. After waw or fa, a sakin lām is a clear sign of Lam al-Amr in this contrast.
5. Remember that a temporary connecting vowel does not cancel the underlying jussive form.
Final practice: لِيَقْرَأْهُ كُلُّ طَالِبٍ وَلْيَكْتُبْهُ — every student should read it and write it.