This video helped me a lot with GI in coordination compounds. As far as Optical isomerism is concerned, its almost the same as organic chemistry, that is, we have to look for planes of symmetry. Only confusing aspect is that in octahedral complexes, you will have to check with all possible planes in the complex because sometimes, when we draw the figure, it might look like its not symmetric but there might be some other plane about which its symmetric. @Chirag_Hegde
PS: I think that book you are referring to is JD Lee. Even I used that itself for optical isomerism. Its explained with many examples there.