Here are my #LightningStrikes tips:

• Look at your migration as more than just face-lifting your existing org to have a new UI.  Think about the end user journey in Lightning and how you can use components in the app builder to accelerate usability!
• Sit with your users and learn about their day-to-day (good for administration in all cases), but do so with the thought of how you can make the experience better with the new lightning toolset.
• Make sure that you leverage component visibility to show or hide components as your users move through a process.  It's super helpful to show something once a certain stage is hit, or if it applies to a subset of users, look at using a custom permission + component visibility (http://www.sfdccloudninja.com/admin/my-favorite-winter-19-feature-lightning-custom-permissions/).
• Have power users test in a sandbox before migrating and turning them on in production.
• If you're a developer and you don't have a component framework already in place, leverage the standard lightning components, e.g. lightning:input.
• If you're a developer and a standard component doesn't meet your needs, make sure you go through lightningdesignsystem.com to make sure you're making a consistent user experience.
• If you have to use classic and lightning, think about using the lightningStylesheets="true" for existing VF and then use lightning out + lightning components for new things (https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/lightning_out.htm).