You can apply for a visa up to 120 days before your intended date of entry (varies by consulate).

For student visas (F1), issuance is limited to 120 days before the course start date.

For tourist/business visas (B1/B2), apply as early as possible—interview wait times vary greatly.

There's no hard rules for your visa application before your planned travel. You can apply for most U.S. visas at any time before your planned travel.