1. Pay for more traffic and hope the laws of statistics hold true because conversion rates won't change.
Paid Traffic Methods:
- PPC (Facebook ads, Google Adwords, Promoted Tweets, etc)
- Solo Ads
- Banner Ads
2. Optimize to increase the conversion rate of the current traffic. (A/B Split Test or Multivariate Testing)
- Google Website Optimizer
- Visual Website Optimizer
Ultimately, there's no "best" option. You either spent money for traffic (saving time) or you spend time testing (saving money). Or both. The choice is yours.