When you create a lead magnet, you should add a tag in your email service provider that names the lead magnet. Then create a welcome sequence to welcome new subscribers to your list.

The series of emails can be sent automatically within most email providers and set up so that whoever signs up for that optin will trigger the sequence to begin. It is up to you how often you send the emails, but the first one should be sent as soon as the first sign up. 

That first email will remind the subscriber of the product they requested, provide link to download and introduce yourself and what you do.

The timing of subsequent emails is up to you. I like to send email #2 2 days after the welcome email, email #3 is sent another 2 days after email #2 and the final email is a week later.

The content of the emails is up to you but it is common to talk about your expertise, tools your use, tips, ask questions and try to engage the subscriber. If you would like a simple script that I use, here it is: WELCOME SEQUENCE

You could also provide additional resources.