Verbs of Assistance and the Dative Case
When you help, advise, or give permission to someone, Russian treats that person as the receiver or beneficiary of your action. This means the noun or pronoun for the person being helped or advised must be in the Dative case.
These verbs govern the Dative directly, meaning you will not use any prepositions before the person receiving the action.
Recommending and Prompting
When giving advice, use the verbs рекомендовать (to recommend) or its perfective counterpart порекомендовать. The person receiving the recommendation takes the Dative case, while the thing being recommended (if there is one) takes the Accusative case.
Another very common verb of assistance is подсказывать / подсказать, which literally means "to prompt" or "to give a hint." It is widely used to mean "to suggest" or to politely ask for directions or information (e.g., "Could you tell me...?").
Allowing, Forbidding, and Hindering
When you grant or deny permission, or when an obstacle gets in someone's way, the person affected is also in the Dative case. Key verbs here are разрешить (to allow), запретить (to forbid), and помешать (to hinder/prevent).
Promising, Refusing, and Contradicting
Verbs dealing with agreements, denials, and opposition follow the exact same rule. This includes пообещать (to promise), отказать (to refuse), and противоречить (to contradict).
Whether you are making a promise to a family member, refusing a client, or arguing with a colleague, that person will always take the Dative case.