Good association means association with one who simply accepts the Krishna as his worshipable deity.
If the devotee feels that, "I can be Krishna Conscious without the association of devotees." it is very dangerous situation. More we separate from devotees, more we bounded by the attacks of Maya. The material world is designed to struggle to exist. So, Srila Prabhupada made the situation minimum by having Krishna conscious temples, communities and farm projects, so devotees can live in association with devotees.
To associate with the holy name and chant the holy name is to associate with the Personality of Godhead directly.
Elevation is possible in Krishna Consciousness in the association of pure devotees who can deliver one from delusion.
Association of saintly persons alone can bring us eternal peace and everlasting happiness and carry us across the ocean of birth, old age, disease and death.
When we keep our association with Krishna, every activity is proper and liberating, but if we disassociate ourselves from the Lord's mercy then like a hand which is severed from the body we become ugly and useless. — In his letter to Hrisikesa, 26th Nov, 1968.