If you've finished reading your textbook, you can start doing past year questions. Try to complete & understand all PYQs, and if you have extra time read some technical articles.
P1 is sub divided in to 4 sections
Study all the parts in turn attempt questions based on each section. Attempt atleast two mock exams.
A lot of past papers questions and I would suggest those ones on ACCA website with examiner's answers which are comparatively the best answers for the preparation of P1 exam.