Here are a few tips to help you to get the most out of the StackSets feature:

• When you design templates that will be used to launch stacks across multiple regions and accounts, keep in mind the specific capabilities of each individual region, since not all services are deployed to all regions. And keep naming conflicts in mind when provisioning resources such as IAM roles or S3 buckets. It's best practice not to give explicit names to resources in templates; rather, you should allow CloudFormation to assign unique names, and then use stack outputs and cross-stack references in order to get the names when you need them.
• Start small with your StackSets, deploying to one region at a time at first, in order to observe whether or not the stacks are successfully created, before deploying to a large number of regions or accounts.
• As with stacks themselves, splitting your StackSets into multiple, smaller templates can make administration much easier. Divide and conquer!