SSMS is really keyboard friendly, and you have keyboard shortcuts for pretty much any functionality that is exposed via the various menus. You can configure them according to your preferences under Tools->Options->Environment->Keyboard. Here are 10 areas that you should definitely be familiar with:
Change Selected Database
Ctrl + U: Once you are in the Sql Editor, pressing Ctrl + U selects the database dropdown in the Sql Editor toolbar. You can then use the arrow keys to change your current database, and pressing the Esc key takes you back to the editor.
Display Estimated Query Execution plan: Ctrl + L
Toggle Results Pane: Ctrl + R
Insert Code Snippets: Ctrl + K, Ctrl + X
Activate Autocomplete: Ctrl + Space
Ctrl + Shift + V: Cycle through clipboard ring.
Navigate in code editor
Ctrl + ]: Navigate to matching parenthesis
Ctrl + –: Navigate to last cursor location
Ctrl + Shift + –: Navigate forward to cursor location
Ctrl + K, Ctrl + C: Comments selected text
Ctrl + K, Ctrl + U: Uncomments selected text
Ctrl + K, Ctrl + K: Toggle Bookmark
Ctrl + K, Ctrl + N: Go to Next Bookmark
Enter Full Screen
Shift + Alt + Enter: View Code Editor in Full Screen
For a complete list of SSMS keyboard shortcuts, see the MSDN article.