6. And learn how to use the ISPF Dialog Test (usually ISPF Option 7) to test your ISPF definitions before actually using them.
Some other suggestions of mine, although others may have a different point of view:
1. Make sure you know and understand the TSO environment. How it works, what it does, what you can do within it.
2. Make sure you know and understand the ISPF environment. How your resource libraries are allocated, and what those libraries are. What resources are you provided for ISPF development. What standards do you need to follow. How do you share ISPF applications across systems and across users.
3. Don't try to combine learning a new language with learning ISPF Dialogs at the same time. Use the existing langauge(s) you already know.