as a rule

bright-line rule

A clear-cut rule, so that it is easy to make a decision.

golden rule

A fundamental rule or principle.

ground rule

The basic rules or standards; basic principles.

rule in

To consider (something) as a possible option among others.

rule of thumb

A general guideline, rather than a strict rule; an approximate measure or means of reckoning based on experience or common knowledge.

rule OK

To be popularly accepted, or supported by the general majority of people.

rule out

To reject an option from a list of possibilities.

rule the day

To set the standard which guides behavior; to control a situation, group, strategy, etc.