Handling elevation changes and switchbacks safely.
Downshift rather than riding the brakes on long descents, since sustained braking can overheat brakes on unfamiliar mountain grades. Give yourself more following distance than you would on flat terrain, since stopping distances change with grade and load.
Check fuel levels before starting a mountain route, since stations can be sparse for long stretches. Weather can shift quickly at elevation, so a route that looks clear at the base can turn foggy or icy higher up.