Your subject line will certainly stand out, and your email will be opened if you make your email unique, useful to the reader, and focused on what the reader either needs to know or wants to know.
You are probably already aware of those things. The following tips may not be so obvious to you.
1. First, you must identify yourself. This means using your own personal name, not some random or misleading name. It is safe to say that all names that are not your own personal name lead to the reader mistrusting you or ignoring you.
2. Remember, each time you send an email you are representing your brand and building brand loyalty. Even if you make minuscule changes such as Adam Smith to John Smith, it still can negatively impact your relationship with your readers.
3. Never misrepresent your email by including misleading comments that have no relevance to a reader's actions ("your order is complete" or "click here for your download link"). Those false claims will undoubtedly lead to readers ignoring you or hating you.
4. Create a sense of urgency every once in awhile. Do NOT say "time is running out1" or "there are only a few copies left!" in every email. Making these kinds of statements all of the time will lead to readers catching on and realizing that you are not telling the truth. In other words, making these statements too frequently will result in readers feeling no urgency at all.
5. Try to condense your emails as much as possible. Remember, the overwhelming majority of your readers will be reading from their smartphone.