Forgetting to pluralize a countable noun or incorrectly adding an 's' to an uncountable noun.
Countable nouns > 1 must add 's/es'. Uncountable nouns (Information, Advice, Knowledge) NEVER take an 's'.
I need some informations.
I need some INFORMATION.
Common uncountable nouns in IELTS: Research, Equipment, Furniture, Traffic, Feedback.