For example, which one of the following sentences can I use?
Consumer of Product X needs to fill out a rebate form […].
Consumers of Product X need to […].
A consumer of Product X needs to […].
This is for a general-purpose announcement.
Countable nouns need an article or similar, if singular:
Generics/uncountable nouns need to be used without:
The second one is the best choice. Or even better, All consumers of product X need to [...].