These are just a few tips I thought up and decided to share:
If you are asked to:
- Describe - state the obvious. Just say what you see and don't explain why it happens.
- Explain - tell the examiner WHY the observed trend/pattern/data is the way it is.
- Describe and explain - do both of the above, but it probably helps to follow up each describing points with its appropriate explanation. E.g: "The graph does A because B. It then does C because D etc." NOT "The graph does A and C and E. This is because B and D and F." It shouldn't happen but it seems more logical to me and plus it's normally the way AQA have written it previously in their mark schemes.
- Explain why ___ was done in the experiment - Make whatever points you feel relevant, but ALWAYS LINK IT TO THE OUTCOME OF THE EXPERIMENT. Often it helps to think 'Ok, what would have happened in the experiment had ____ not been done?' then answer from there.
- Evaluate - Write a balanced argument using your own biological knowledge applied to the information in the question. If it helps, write bullet points. Describe and explain the pros followed by the cons (or for/against etc. dependant on question context) then follow up with a sound conclusion.