The answer is: it depends.
Noone can really give you a 100% accuracy answer.

Marketing is all about experimentation, people surveyed different checkout pages and every industry seems to find different results - mainly because their audiences differ. (Age groups, etc)

With email, it's much of the same. That said, here are some tips:

*Headlines*
By far your most important piece to email marketing.

Do a small A/B test for the headline to maybe 10% of your mailing list. Your headline is by far the most important part to email marketing - weak headline, low open rate.

*Personalisation*
Emails coming from a "person" as oppose to a company do really well. And if you can, always address it to the individual (first name etc).

*Email length*
This really depends. You see long sales letters do well, you see short and snappy emails do well.

It depends on the action/service/price you're asking the user for. If it's a free app, as commitment is minimal you can probably keep it short.

If it's a paid app, you may need a follow up sequence and a longer email (or video).

If you provide me with a little more detail, I'm sure I can help - if you even just drop me a message with a little more info about:
1. Your product
2. Your email subscribers (Where you obtained them)
3. Your price point
4. The problem you are solving
5. Any demographic data on your users

I can help you with some more detailed recommendations.

I hope that helps.

Thanks,

Nitesh

1. Emails That Establish Positive Relationships
Congratulations! Your just got a new email subscriber. Now it’s time to establish a relationship with them.

And what is every great relationship built on? Trust. This should be one of your main goals when crafting your promotional emails.
When you first sign up to OptinMonster’s newsletter, you receive a welcome email from “Syed from OptinMonster,” our co-founder.

Using Syed’s first name adds a personal touch to the email that helps it sound less like it comes from an entity and more like it comes from a colleague. The tone of the email further supports this feeling by being cordial yet professional, as if it’s coming from a knowledgeable friend who is interested in helping you.

Before diving into business, Syed takes time to personally thank the reader for subscribing, using phrases like “join us” and “welcome to the family” to establish this is not just a newsletter, but something bigger. And now, as a subscriber, the reader has become part of it.

This welcome email example does a great job of introducing Syed’s brand and laying down strong groundwork for a relationship with the reader, but he takes it one step further by promising his reader helpful premium content as a “thank you” for signing up for emails:
In the above screenshot, Syed promises three future gifts for his reader. And over the next three days, he delivers on them.

Keeping this promise helps to establish trust and shows Syed’s readers what they’re getting from the relationship right from the start.
Key Takeaways

Here are a few ways you can write a stellar email similar to OptinMonster’s:

Using your personal name, if it’s appropriate for your particular company, can add a personal touch to your emails
Thank your reader for their time
Set expectations and stick to them
Make promises and follow up
Offer value to your customer early and often, showing the benefit they can expect to receive from this new relationship
And speaking of which…

2. Emails That Offer Readers Something of Value
Offering your audience something that will be valuable to them does a few things:

Catches and holds their attention
Endears them to your brand
Encourages them to purchase/interact with your products, services, or website
Since you have a product, service, or content you’ve painstakingly created for them, offering your readers something of value should be easy to achieve. Simply offer discounts on your merchandise or services, or promote some of your great content.

These next two emails do this really well:

If you’ve got great content, flaunt it. That’s what List25 does.

Your email newsletter is a great opportunity for you to keep your readers up-to-date on with the content you’re producing. Provide a highlight reel and explain how these posts can help your readers.

Of course, nothing entices readers more than getting a great deal.

Promoting Discounts in Email Marketing
Offering your audience a valuable discount has the power to convert unsure readers into faithful customers. In the example above, Walgreens speaks to the bargain hunter in each of us by offering a 20% coupon.

Key Takeaways

Here are a few things you can do to your promotional emails to make them more valuable for your reader:

Don’t simply try to sell; instead, share free content you’ve produced
Explain how your content will benefit your reader by solving a need
Offer your reader valuable coupons or discounts
3. Emails That Capture The Audience’s Attention
You have a limited number of characters to catch your reader’s attention and convince them to open your email, so make them count!

Just because your audience has already shown interest in what you have to say by subscribing to your list, you can’t become complacent. With each new email you send, you need to recapture their attention and entice them to stay engaged with you.

There are a few ways you can do this. In this example from Social Media Examiner, the problem the email promises to remedy can be found in the subject: improving the reader’s Facebook reach.

Captivating Subjects in Email Marketing
Whether you’re selling a product, a service, or a blog post, titling your emails to address a specific need of your audience is a great way to grab their attention and convince them what’s inside your email is worth their time.

The subject gives just enough information to pique the audience’s interest without giving away the whole story. If the reader wants to find out how to say goodbye to their lackluster Facebook reach, they’re going to have to open the email.

If you’re offering your customer something valuable, highlighting the value in your email’s subject is a great way to get people to zero in on your email and pick it out of the dozens of other promotions they receive every day.

Another good example of a captivating subject is the Walgreens email we saw earlier:

Captivating Subject Lines in Email Marketing
By using compelling phrasing like “Today Only,” Walgreens creates a sense of urgency and entices their readers to open their email right away or risk losing out on the deal. Walgreens knows how easily non-urgent “to-do” items can slip through the cracks and be forgotten, so they craft their subjects to encourage swift action.

If your business relies on website traffic to generate sales, getting subscribers to merely open your emails is only half the battle. You need to get them to click the link in your email and visit your website.

Jon Morrow takes a “less is more” approach to accomplish this task.

The subject of his email simply announces the publication of a new blog post. And once a reader opens the email…

Minimalism in Email Marketing
…they see a wall of white space.

Jon teases the problem the blog post will seek to resolve, and then he offers a link to click.

That’s it.

There are no images, no distracting commentary, and no fluff. He doesn’t want anything distracting the reader from the task at hand: clicking that link.

Key Takeaways

Some takeaway points that you can use to increase your chances of readers opening your emails:

Present a problem the email seeks to solve
Make the subject short and impactful
Lead with the value you are offering your reader
Use urgent language
Concisely state the value of your content in the subject
Avoid fluff
4. Emails That Know Its Audience
Depending on what you’re promoting, your audience will expect different things from your emails.

It’s important to have a clear goal in mind for what sort of image you want to present, so that you can make sure it is clearly coming across in your emails.

Here are two effective, yet very different, promotional emails finely tuned to their respective audiences:

This s a really great question. I've done email marketing for multiple 7- to 8-figure companies, and here's the secret...

There ARE trigger words you can use to increase sales, and increase your results.

I love the subject line tester from Send Check It (no affiliation): https://sendcheckit.com/email-subject-line-tester. I use it myself to test for subject lines before sending, and it works very well.

I also highly recommend you make sure your tech stack is set correctly. Before you send an email, make sure your SPF, DKIM, and (maybe) DMARC are set up correctly. Your web host can help point you in the right direction. This will help make sure your email actually gets delivered! Even the best messaging in the world won't matter if you're running into delivery issues, and ISPs are cracking down on unauthenticated emails more nowadays.

For body copy/text, emulate companies that you like. What email newsletters do you subscribe? Copy them. If they're a successful business, chances are they've optimized their email copy and layout quite a bit.

After you've drafted your email, I also recommend the site mail-tester.com (again, no affiliation, I just like their tool) to make sure your email body copy isn't too spammy.

Also, I highly recommend one week later sending the email to all non-opens. We've noticed ourselves that re-sending to non-opens with a new subject line and maybe slightly adjusted copy will often result in a ~10% open rate. In other words, more traffic for a very minimal amount of effort.

Finally, the length of your email and the type of content you feature really does depend on you, your brand, and your audience. Do you LIKE writing long emails? Is your other email content long, or short? I've seen both work very well, and it's often a preference of the copywriter.

What I do think is valuable is, for a big launch, don't just rely on sending an email. We use a "content multiplication" concept where we feature a product launch EVERYWHERE — we send an email to our list, we email our friends, we run a giveaway, we post on social, we do some FB ads. The more places you can get your product to show, the better the results.

Hope that helps, and good luck.