Hiya - my teacher has thankfully given us quite a bit of time/advice on the NEA. These are some small but helpful tips:
1. Never use first person (i.e. I/we/me). Try to sound as academic and impersonal as possible (so like: 'The questionnaire was done in site x', rather than 'I carried out a questionnaire in site x').
2. Keep an up-to-date plan of everything you're going to do for your investigation.
3. Focus on the question and be specific- how does what you've done actually help you answer your study question?
4. Try to put in some models (you can look these up, they dont necessarily need to be from the A-level spec).
5. Formatting matters! Try to make it readable and easy to understand.
Hope this helps!