In order of speed for a service business: (1) your past customers. A reactivation email or text to people who already trust you closes in days; (2) referral asks to your best current customers, made personally; (3) Google Search ads on emergency/high-intent terms, live within 48 hours if your tracking and landing page exist; (4) answering every review and inquiry FAST. Speed converts demand you already have.
Note what's not on the list: SEO, social growth, branding. All compound beautifully and none reliably produce customers in 30 days. This-month problems get demand-capture answers.
The uncomfortable audit that often beats new spending: count last month's leads that never got a same-day response. Most businesses fund a leak instead of fixing one. The fastest new customer is the lead you already paid for, answered faster.