Having a smart call to action at the end of each blog post is generally a good practice. Make it stand out, and make sure to add value to the visitor by signing up.

I strongly recommend A/B testing (also called split-testing) your sign up call to action. That's the only way for you to improve the results of the signup rate.

In regards to the conversion rate it's extremely difficult to predict. Depends on your value proposition, quality of content, your industry and so much more. Best advice is just to get started and be smart about the a/b testing.

If you are running Wordpress I can strongly recommend OptinMonster to manage your call to actions. Unlike other solutions you won't have to pay a fortune, and it's very good.

I'd also like to throw some flame to the fire on the ever ongoing discussions about popups. They receive a lot of flak, but are extremely effective. You can expect up to 200% more signups by using exit intent popups. Again - make sure to offer value to the visitor.