It's often a good strategy to allow users to subscribe to more than one list in a newsletter subscribe form, a kind of 'upselling' of your other email lists if you like.
Here's how to do it in Zoho Campaigns.
Click the Contacts tab, then...
Select the list you want to add more options to, for example "Newsletter".
Click Sign-up form, then...
Edit form fields
Add another mailing list to this Sign-up form.
Select New Mailing list (see below).