Social media traffic in general tends not to convert directly to sales, because most people use social media sites for entertainment and not for shopping. Pinterest tends to have a higher shopping intent than other social sites, but still expect a low conversion rate.
There are two things you can do to improve your conversion rate: improve your leads and improve your site.
To improve the quality of your leads, try putting a price tag on your pins in Pinterest. This will tend to attract people who are actually shopping for something, instead of just browsing pretty pictures. Make it clear that the item in your picture is something you have for sale. Use buying keywords in the pin description. All these will attract people to your pins who are more likely to purchase, leading to a higher conversion rate.
As far as improving your site, for reducing bounce rate you can include a "related products" widget to your page, with pictures of other products the user may be interested in. Pinterest users are very visual, so make sure your site design looks nice.
As for improving e-mail conversion rates, don't just ask people to sign up, offer them an incentive. The exact incentive will depend on your industry, but make it something that complements whatever it is you're offering, like a free guide or tip sheet. If you can't think of anything creative, try offering a one-time 15% off coupon for signing up for your newsletter. Make the sign-up form a popup, so people can't ignore it.