Delighting your clients is always rewarding to you both.
Give “lucky bags” to clients when they finished buying and are about to leave (you can have a minimum transaction size.) These do not have to be expensive, but more of a novelty, and have more than 1 or two kinds. You can use these offline and online (by offering a selection of “bags” to choose from.)
Try a new way to make the opt-in sequence convert better.
Let them read (by simply clicking) the first page of what you promise them in exchange for their email and only then ask them to opt in. This, of course, should sell the whole product you are giving them for free.
An experiment for a new way to get better conversions.
Instead of promising the visitor something in exchange for their email address (like a free report), simply promise them a personal connection with you – whenever they reply to an email you send them you will personally (or another human and not an automated system) always reply quickly.
Social proof – show them others also think it’s a good place to be.
Use software to show small images of people floating on the page (in the margins) at the section they are reading now.
Document and quickly reference your work in the future when you need inspiration.
Use a content management system (can even be a private WordPress blog) to store the swipe file you write: emails, landing pages, etc. Tag each with the specific descriptors, so later when you need inspiration, you can easily and quickly find old/new ideas.