Bhagavad-Gita 18.66 says that we should abandon all varieties of religion and surrender to the Lord. We find that in the case of demigod worshippers they are attached to meat eating and other vices, even when they start chanting a round a day, the level of surrender is not really very high. What should we do?
The particular verse you have quoted is one of the final instructions of Lord Krishna to Arjuna and requires a high level of faith and surrender. Krishna also says that one must not disturb the faith of other people as they may lose whatever little faith they have in Vedic knowledge. Rather than asking new devotees to give up demigod worship, meat eating it is more expedient to ask them to add Krishna to their lives and let the process of devotional service cleanse their material desires.
What sort of heart and qualification required to completely surrender to a spiritual master?
Krishna describes in Bhagavad Gita how one should approach a realized spiritual master (Bg 4.34). He indicates three components: submission, inquiry and service. One should approach the spiritual master with all humility, hear from him submissively and inquire from him to get a clear understanding about the spiritual science. Inquiring alone is not sufficient, but one must also render service to the spiritual master according to what one has heard and try to please him. One should be prepared to render menial service to the spiritual master and follow his instructions.
If one is very sincere to know Krishna, He will send His mercy in the form of a representative, to provide exactly the kind of spiritual upliftment the soul requires.