In terms of the software tools you can use to build an opt in page, there are many options available.
I use LeadPages because it's quick, easy and very affordable.
They specialise in creating landing pages.
They know what works and their pages always look clean and professional.
More importantly, they get good opt in rates.
You can also include an image on your opt in page...
It can help a little to convey what people are getting as the freebie.
You can show people what they're getting or a visual representation of it, and test it yourself.
This teases people a little and evokes their curiosity.
They want to get their hands on what they see.
Make sure you use the same messaging and angle throughout your email list process;
This means the wording used in the headline, on the button, on the thank you page and inside your first email.
For example, don't say in the headline;
"Download this x y z."
But then on the button, say
"Get access to ABC."
And then in the email, say;
"Thank you for subscribing."
Use the same wording, and messaging throughout.
You've now got everything set up.
So it's time for the final step...