Suggestions for better metadata management:
1) Use 20 simple and accurate terms.
2) Disambiguate all terms. Check for accuracy. Do not duplicate terms.
3) Batch keywording: Review every file in the batch for accuracy before uploading.
4) Do not use trademarked terms for creative royalty-free imagery. They are acceptable for Editorial content only.
5) If you are copying another contributor's keywords, please don’t because they may not be accurate or suitable for your image.
iStock articles on keyword management: