30 most common words beginning with pre-?

It's impossible to definitively say which 30 words are the "most common" as that depends heavily on context (like the type of text you're analyzing, the specific dialect of English, and so on). However, here are 30 words starting with "pre-" that are very common in general use:

General Use:

1. pre- (prefix)

2. pre-existing

3. pre-empt

4. pre-mature

5. pre-order

6. pre-paid

7. pre-school

8. pre-requisite

9. pre-teen

10. pre-war

11. pre-flight

12. pre-game

13. pre-determined

14. pre-recorded

15. pre-owned

16. pre-natal

17. pre-production

18. pre-emptive

19. pre-eminent

20. pre-historic

21. pre-maturely

22. pre-selected

23. pre-occupied

24. pre-planning

25. pre-med

26. pre-season

27. pre-surgery

28. pre-authorize

29. pre-interview

30. pre-approval

Note: This list is not exhaustive, and the ranking of "most common" can vary depending on the specific context.

For a more precise idea of common words, you could look at word frequency lists for specific types of texts (like news articles, fiction, or academic papers) or analyze large corpora of text.