Personally, I'd just dive in and try to make something that interests you. Either something you have already done in VB (just to sort out the coding differences) or something all new to try.
It never hurts to read all of the various tutorials and try different samples, but I think you gain the most experience from real-world stuff (in this case, writing an actual functioning app).
For my first app, I chose something that I had essentially already done before in VB6 and applied it to a mobile platform. Part of my reason for that was to learn how to use B4A and believe me, I learned quite a bit in the process. While I didn't cover every feature available in B4A, I covered quite a number of core things that you need to know to make any typical app in B4A.
Good luck and have fun! I taught myself VB as well, and my interest in programming all started with teaching myself BASIC on the Commodore 64 about 26 years ago. Ahhhhh, memories.