The Rules of Popup Implementation

Popups are an agressive and often abused tool in a marketer's toolbox.
Below is a list of rules to adhere by to make sure your popup isn't overly disruptive to your site's visitors.
Browse our Popup Wireframes.

Stick to the brand.
Don't use colors and fonts that clash with the main brand. Stay on brand to minimze disruption.
Don't use offputting or sarcastic language.
A common trend is to use crude or offputting language around the close action of the popup to guilt people into converting. This frowned upon by most UX best practices.
Don't hide the close button.
Users are coming to any given website using different devices and with varying levels of browsing experience. Don't make them look for a hidden close button or link. Make it noticeable and easily clickable.
Disable on mobile.
Mobile popups are the devil. Period. Disable them on any mobile devices where the viewport width is < 768px. Also of note - Google frowns upon mobile popups.
Keep them simple and concise.
Don't make a user read an endless amount copy about your newsletter sign-up. Be short and brief.
If a user closes it or opts-in - make sure they don't see it again.
The only thing more annoying than a popup is a popup that will not go away.
Run 1 at a time.
Don't run more than one popup offer at a given time. This is especially true if your popups look similar - users might think that the same popup is annoying them over and over.
Give them a master opt-out.
Sometimes users will never want to opt-in to your offers. Give them a means to opt out of all future popups on the site.
Keep forms short.
I know - you want to capture that users information for your latest e-book/webinar recording. Only ask for the bare minimum information (*cough*email*cough*). Respect your users time.
Only show them where it makes sense contextually.
Don't show a user a popup about a newsletter on their homepage. Likewise don't advertise an e-book about "cheese" on a page not talking about "cheese". The less relevant the popup is around the current content - the less likely a user is to convert.