Once I have had set up my emulator of choice, I really wanted to try some BASIC programming, like the old times. I recall the INPUT magazine being a great source of information, at least here in Brazil. It covered BASIC programming, the basics of coding games and even some machine code. INPUT was a great collection and helped many people to start programming in early ages. Oh, boy, I used to read each issue from cover to cover, even the sections related to other machines. Thankfully, the entire collection is available here.
Will Stephenson in the Spectrum Next facebook group shared a link to some free programming books from the 80’s by Usborne Publishing, which can be of some interest too.
There is also a new book called ZX Spectrum Games Code Club, which seems to be a good resource for brushing up old BASIC skills. I will probably take a look into it soon.
At last, I also recommend joining the Basic on the ZX Spectrum group on facebook, as a way to make new friends and improve your knowledge by participating in the programming challenges.