‘Literary criticism can be no more than a reasoned account of the feeling produced upon the critic by the book he is criticising.’
D. H. Lawrence

Just do it: I think a good guide is; write the outline of the book, what you personally got out of reading it and whether you think other people should try it.

Make SN your writing practice / class. Worse case everyone hates the book but they are unlikely to hate an honest review.

And take heed;
‘In certain kinds of writing, particularly in art criticism and literary criticism, it is normal to come across long passages which are almost completely lacking in meaning.’
George Orwell

I think you're being overly modest. You express yourself better than most of us on here.