BASIC was intended to be baby's first programming language, so it is very simplistic, but it teaches you some bad misconceptions about programming, so you have to actively re-learn when you're switching to something better.
Also, there were tons of implementations, each one slightly different from each other, so eveb your BASIC-related knowledge was useless outside of one platform.
Install an antique machine emulator (ZX Spectrum, Commodore 64 or Apple II), find scans of a book teaching BASIC that went along with it online and type out the examples, but don't spend more than evening on it.