In order to know if your emails are effective or not, you will want to look at the open rate. This open rate can vary per industry, so you might want to do a quick research on your industry to insure you are where you need to be.

For me, a good open rate is about 50% for the first email

and once they have been in the system for a while depending on your industry, a good open rate is around 30 - 50%.

Your subject line will determine the open rate of your email so don't chince out on this.

Take a moment to study other emails, evaluate them, and execute them.  This is really important to take a moment to make sure your subject headline is intriguing and curiosity-creating enough to ensure that your leads will click to engage with your email.

If you love to get ideas, go ahead and opt into other sponsored posts that are similar to your market and see what types of emails they are sending you.

Practice will help to make it more perfect.

If you would like to read more about open rates, you can check what Aweber has to say about this.