Starting small.
WHY START THERE
Most visitors are on phones.
WHAT THAT DISCIPLINE PRODUCES
Prioritisation, because there is no room for everything.
WHAT IT PREVENTS
A desktop design crammed onto a small screen.
WHAT TO DECIDE FIRST
What matters most, since it must come first on a narrow screen.
WHAT TO ADD AS THE SCREEN GROWS
Space, and secondary content beside the primary.
WHAT NOT TO ADD
Things that were not needed on the phone.
WHY
If it was unnecessary on mobile, it is probably unnecessary anywhere.
WHAT TO AVOID
Hiding content on mobile that desktop users see
WHY
Search engines and many visitors see only the mobile version.
WHAT TO TEST FIRST
The phone experience, on a real device.
WHAT TO CHECK
That the primary action is reachable without scrolling far That text is readable without zooming That targets are large enough
WHAT TO MEASURE
The proportion of your own visitors on each device.