Formal:
* Comply: This implies following rules or instructions obediently and without question.
* Obey: Similar to comply, but emphasizes submission to authority.
* Conform: This implies following established norms or standards.
* Adhere: This is a general term for sticking to something closely, including rules.
* Abide by: This means to accept and follow a rule or decision.
Informal:
* Stick to: This is a more casual way of saying "adhere to."
* Follow the letter of the law: This emphasizes strict adherence to the exact wording of rules.
* Be a stickler for the rules: This implies someone who is overly concerned with following rules precisely.
The best word for your specific situation depends on the context and the tone you want to convey.