Question: It is said that it is not good to serve Krsna directly. Can you exlpain me how does a person act who wants to serve Krsna directly?
Answer: To directly serve the Lord is only possible in a pure state of consciousness and by the mercy of Krsna. So trying to serve the Lord directly is not the recommended process to purify our conditioned consciousness. If we try to serve the Lord directly, the Lord may be served or may not be served. The way to assure the service to Krishna is by serving His devotees, the Vaisnavas, His representants in this world.
In a Vaisnava we find the knowledge and love of Krsna because as he is surrendered to Krnsa, all his activities he preforms for Krsna. That's why a devotee, or Vaisnava, is very dear to the Lord. So the best way to become engaged in the service of the Lord is to accept a spiritual master and try to do some service for him. In this way our service will be connected to the disciplic succession (parampara) of Vaisnavas and in this way reach Krsna.
The Lord himself said: The one who renders service directly to me is not my devotee, the one who renders service to my devotee is my devotee. So the idea of serving Krsna directly and independent from others means to ignore the instruction of the Lord and to ignore His devotees. But the devotees of the Lord are very dear to the Him. Krsna is not cheap, we cannot force Krsna to accept our service. If we want to serve Krsna we have to consider His devotees.
To accept a spiritual master as the guide of life and to render service onto him and the devotees is essential in spiritual life, because if we accept the Lord's devotees as greater than ourselves, we will also be able to accept that we are very small and insignificant before the Lord. Therefore we should always keep Krsna and the Vaisnavas dancing on our head.