Teh DSA thoery test book is a good idea - go through each question in tyhe book (there are lots!) and on a piece of paper make a note of all those you got wrong or struggled with. Then go back and practice these questions until they are fine.
That’s the method I used and managed to get 35/35.
There are DVDs available for sale (or from ‘places’ online) where you can run mock theory and hazard perception tests - these are a must too.