How do I create a global keyboard shortcut to create a new note in Notes.app or Reminders.app? The new Notes app is great but How do I create a new note without switching to the Notes app first? 

Same goes for Reminders.app.
Reminders

You can create a service using the Automator:


Open Automator.app
Select Service
For Reminders: Add action Ask for Text to prompt for a new To Do
Add action New Reminders Item
Save Service
Create Shortcut in:

System Preferences &#x2192; Keyboard &#x2192; Keyboard Shortcuts &#x2192; Services &#x2192; Text




Notes

See Mohamad Elwan's answer for notes