Final answer:
The initial step is to inspect the roof deck for damage and make necessary repairs.
Step-by-step explanation:
The initial step when starting to install asphalt shingles on a roof is to inspect the roof deck for damage and make necessary repairs. This is important to ensure a stable and secure foundation for the shingles. Once the roof deck is in good condition, the other steps can be followed, such as applying underlayment, installing drip edge, and snapping horizontal chalk lines to guide the shingle installation.