Visit forums related to your niche, have a look around them and see what people are talking about. Remember to listen before you speak. Set up your profile. Add value by answering some questions. Engage and if you see a thread where you think you can add value post a reply to that thread. Be sure to observe the rules of the forum or you may get banned.
Now, you can automatically send highly relevant emails encouraging them to buy the product or service they were considering. Customers who received multiple abandoned shopping cart emails are 2.4 times more likely to complete the purchase than those who receive only one followup email, according to Experian. Try sending the first message one day after, a second message 48 hours after, and possibly a third message within three or four days of abandonment.