Using certain words in your subject lines can encourage people to open the email.
Mailchimp’s set of popular words coming from a dataset of over 9.5 billion emails: posts, jobs, survey, week’s, e-newsletter, issue, digest.
Hubspot’s top 7 words pulled from data from over 500,000 emails: secret, e-sales, awesome, skills, ebook, helpful, shipping.
Source: www.mequoda.com