Formal:
* Announces
* Proclaims
* States
* Pronounces
* Avers
* Affirms
* Asserts
* Maintains
* Decrees
Informal:
* Says
* Says outright
* Lets it be known
* Makes known
* Speaks out
Other:
* Defines (if it's about setting something out clearly)
* Specifies (if it's about giving detailed information)
* Contends (if it's about arguing a point)
The best synonym for "declares" will depend on the specific meaning you're trying to convey.