I’ve noticed that many Greek letters have the same pronunciation: (υ,η,ι, ει, οι) and also (ε, αι), and possibly others.
Even though I can pronounce Greek words easily, I am having great difficulty writing them correctly.
What is the best way to learn Greek spelling? Any tricks, hacks or shortcuts?
I think there is no shortcut. There are certain patterns which you will certainly discover yourself during your studies. Among the activities on lingq, you could try dictation.
You need the rules of grammar for the endings of the words and etymology for the roots. For the English that I’m learning, I need the same!