1. Navigate to Documents.  You will see a listing of all your files. 
2. Create the file to share if you haven't already, then close out to get back to your file listing page.
   
3. Click the check-boxes next to each file you would like to share.
4. Click the share button.
5. Click "choose from contacts," which will bring up your mail address book (individuals and groups).
6. Choose the list of people you want to share with (or choose a group, by clicking the down arrow, if they are already organized together into a group).
7. Once you have your new list of people, you can save them as a new group with the "save as group" button.  You might need several similar groups (e.g. "LGT plus Sarah and Tim"). 
   
8. Click done.  Whether or not you send invitations, the files will show up in each person's file listing. 
   
9. So, by clicking many file check-boxes and then sharing with a preselected groups, you can share many files with many people quickly.

You can also share from within a document using the share tabs in roughly the same way (steps 5-8), except the procedure above will allow you to share any number of documents at once.