に限る: the choice the speaker considers best
Understand a strong personal preference without mistaking it for a restriction or official obligation.
An evaluation that this option is best
休日は静かな公園を散歩するに限ります。 means that nothing beats taking a walk in a quiet park on a day off. The speaker confidently singles out a particularly good option among possible activities.
限る does not establish a rule banning every activity other than walking here. Unlike a notice imposing a restriction, this use focuses on praising a choice that fits the situation.
Present a thing or an action as the choice
A noun can attach directly, as in 暑い日は冷たいお茶に限ります: nothing beats cold tea on a hot day. 暑い日は冷たいお茶を飲むに限ります uses a dictionary-form verb to present drinking cold tea as the best action.
疲れたときは無理をしないに限ります。 means that it is best not to push yourself when tired. The negative ない-form can also attach; the recommended choice here is restraint rather than performing the action.
Compare に越したことはない
荷物は軽いに越したことはありません。 means that it is better for luggage to be light if possible. に越したことはない acknowledges a preferable condition without necessarily insisting that it is the only acceptable option.
に限る puts the speaker's preference for a particular best choice more prominently in the foreground. Both expressions can offer advice in context, but neither alone creates an official obligation or prohibition.
What choice does 疲れたときは無理をしないに限ります。 recommend as best?
Show the answer and why
Not pushing yourself when tired. Keep the negation in しない; reading it as a recommendation to push yourself reverses the meaning. It evaluates a preferred approach rather than issuing an official ban.