Thank you - very helpful.
Current level: Beginner. I understand the basic concepts of differentiation, the rules of derivatives etc. But no prior knowledge of integral calculus or multivariable calculus.
I take it your advice is still valid for such knowledge level?
Yes. Have more than one book at hand. Apostol's books seem to be still available, albeit published in India (which means low-grade ink and paper). Still, each of the two volumes is under $20. Also get the Schaum Series "Beginning Calculus." You already have Lang. I also like Banner's "The Calculus Lifesaver." For multivariable you will need some additional books (other than Apostol, that is), as well as some background in linear algebra.