since you have a skills test coming up (100% skills as opposed to 20%skills + 80%content), I will give you tips on studying biology skills. before my skills test, my teacher told us that she would try her best to NOT include any content-based questions to ensure the exam is PURELY skills. this means that memorising notes and reading textbooks won't help for a skills test. instead, you need to be consistently practicing skills questions. these may include:
- drawing scaled diagrams
- graphing (know when to use a line vs. column/bar graph, ensure you have a title, labelled axes with units etc.)
- method-writing (methods for models, first-hand investigations and epidemiological studies have different structures, ensure you address validity, reliability, accuracy)
- go over what makes an experiment AND a source (primary/secondary) valid, reliable and accurate
- pedigrees and punnet squares
- allele frequencies
- other scientific report elements (know how and when to write an aim, hypothesis, conclusion)
I suggest looking for such questions in past HSC exams, trial exams (if you have access), books etc. Personally, I prepared for my skills test by doing past HSC questions. if you manage to do all the skills questions from every HSC exam while correcting and refining your technique (+speed, timing can mess with you), you will be more than ready. it's really a matter of practice and exposure to the many types of skills questions out there. preparing for skills exam = do skills questions
Hope this helps!