Are you looking for someone to actually make a purchase, it’s just product or brand awareness, why are you looking for overall site traffic.
Sometimes a newsletter sign-up could be a very powerful tool to convert a suspect to a prospect. Will cover platforms for email marketing later but always consider when you are getting someone’s email address what are you giving back in return. I’m sure you’ve seen sites that have a free book or a book and if you fill out a form they sent your email you and let you download a copy this is a good give-and-take to get someone’s information.
There’s the classic pop-up box to request someone’s email address. This can be very effective but depending on your overall goals could be slightly annoying and if you’re planning on achieving a high end look and feel a pop-up could grade the value/quality of your website.