Because you have given them something of value for free, they are more likely to trust you when you suggest products for them to buy. The success mailing list of your free report relies on you creating a good quality report with useful information. If it is just a sales page for a product, you will lose people off your list as fast as you can add them. If your subscribers like your information, they are more likely to share it with friends and colleagues.
Each copy of your free report goes out into the world with your name and your links attached. You can build a silent army of promoters without it costing you anything more than a few hours of your time. You want to set up an opt-in page to mailing list build your list. You need to decide what you are going to offer to get people to sign with you. Your incentive has to be valuable to your potential subscriber. They need a good reason to give you their email address and name.
There are a few popular options. Some examples are an e-course, an e-zine, a newsletter, a blog, a special report, or regular emails. Emails are probably your worst option because they are often deleted without being opened. How many emails mailing list do you get each day? Unless your emails are very eye-catching, you should probably not use this option. An e-course establishes you as an expert in your field.