Email open rate is the percentage of subscribers who open a specific email out of your total number of subscribers. The success of your email marketing campaign depends on email open rate. Every person who doesn't open your email doesn't see your offers.
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The Subject Line - use 6 to 10 words in your subject line; if a subject line is too long, it will get cut off (especially for mobile users) and your reader will not know what the email is about and could ignore it. Again, personalize subject lines with the reader's name.

The Sender Name - use a specific personal name rather than a general email address or company name.
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The Timing - timing can have a huge effect on whether or not your subscribers open your emails, so think carefully about what time and day you send your emails out. The timing depends on the location, age and occupation of the recipient.
Perform A/B test to identify the best time

Keeping your email open rates high helps to protect your sending reputation. If your sending reputation declines, your emails will hit the spam and promotion folders which can seriously affect your sales.