Your marketing (advertising) message should attract potential customers filtering fans of free. It is desirable that the value of your offer was higher than what you ask for in return. You give some product for a minimum price or even free to get contacts. To make it difficult to refuse the offer.
You need to analyze competitors and find out what they offer to make your offer stronger. You can strengthen your offer in many ways. Gifts, discounts, promotions, sweepstakes, lotteries, customized offers, delivery speed, shipping cost, amazing service and so on.
As a gift, you can give a mug, t-shirt, cap, book, booklet, fridge magnet and so on. If at the same time the cost of a gift is high, you can put in the condition of the purchase of your products for a certain amount for example. Also on your gifts can be placed your advertising with the logo and slogan of the company. View, as it does Burgerking, giving free crowns from their advertising or balls.