If you turn on the Print List" strategy you will find a little print icon on top of your lists.
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Click this icon to open up the print overlay. 

In the print overlay you can see your list and expand/collapse any nested items to make sure you are printing exactly what you want. 

Once all the items you need are showing and you are ready to print, click the print icon in the very top left to get to your computers print dialog. 

Change any settings you need here and click print. 

You can currently print 

To print a project or category, go to the fullscreen project/category view and click the print icon at the top right of your task list.

To print a Smart Lists, either go to the Smart List overlay (through the menu at the top right) and click the print icon next to the list.

Or if you want to see the Smart List first, go to the Master List and open up the sidebar ("X"), go to the Smart List tab and click on the Smart List you want to print. There will be a print icon at the top right of the list.

In the future you will also be able to print the calendar views and your week overview.