The vow one should take before initiation is exclusive devotion to your Guru and Bhagwaan.
The first initiation is Harinaam Diksha, and there are no additional rules except a commitment to chant Harinaam as much as possible.
It serves as your entry into this spiritual path, similar to how a child begins their education in nursery or kindergarten.
At this stage, you gradually learn the foundational teachings. Over time, with the Guru's blessings, you may progress to the second initiation, where you receive the mantra to worship Radha and Krishna at home through altar worship.