If you can understand the intricacies of C and C++ (manual memory management, preventing use after frees etc) then SQF will be easy for you to learn - it's managed after all. The main advice I can give you regarding learning SQF is to research how ArmA's scheduler works [1], and how ArmA handles (or, the lack thereof) of Lazy Evaluation [2].
On top of this you will have to get accustomed to a significantly restricted language, no maps/key value/dictionaries (at least, not natively - you can emulate them), no classes etc.
The language is definitely showing it's age and Enforce is hopefully going to change that when the next game in the ArmA series comes out.
If you want a good starting point, I'd recommend checking out the public Altis Life repo and seeing how the built in scripts work, then try making modifications, then building up to creating new features / systems.