Speak their language and start with common themes;

• Hierarchy
• Pace
• Space
• Ratios
• Grid
• Typography
• Colour
• Legibility / accessibility

Highlight what's different

• Fluid canvas (no fixed size, people scroll)
• Layout needs to accommodates various devices (responsiveness)
• Interactions
• Think journeys rather than pages
• Being modular

Learn from others

• Observe design choices
• Get them to think about their own online experiences
• Study design guides and how they're applied

Just do

• Apply what they already know
• Experiment with the bland and the bold
• Think beyond a flashy landing page, think about long-form content
• Get them to open flat designs in a browser to see designs in-situ (much like printing a page to see if it visually works and the right choices have been made)
• Use the tools you want
• Start to learn the new tools

Whilst not specific, it's a pretty good list of topics to cover in my opinion.