The quickest way to generate sales leads is to build a strong referral network. People buy from people they know and trust. If you can get a referral from a trusted source, you have a much stronger lead.
Think about related products and services your potential customers might need. For example, if you sell roofing services, you could exchange leads with companies that sell windows.
You might also ask around your city about any lead exchange groups that you could join. These groups get together about once a week for the sole purpose of providing sales leads to each other. If you don't know of such a group, check out BNI. They have chapters throughout the US.