You are asking your readers to engage within your site, and this is essential if you are looking for any kind of end product (maybe a sale?) from them.
Offer the chance of engagement and convert your audience into action takers.
The obvious progression is a “buy now / order now” function, but there is so much more that you can offer.
Competitions are great for building a connection between you and your audience. The same can be said for freebies – free advice, free design templates, free recipes.
Signing up for your Ezine or RSS feeds is another example of somehow retaining your possible reader (customer).
It all comes back to the Audience being the important factor here. Offer something of worth to them and they will keep coming back.