What keyboard actions can I take to navigate the command line?

A. Rather than just using the left and right arrows to move one character at a time through the command you can also use the following

You can also use the Tab key to complete filenames for you as described in Q. How do I enable Tab to complete file names?

If you enable QuickEdit on command windows (Right click on the title bar, select properties, Options, QuickEdit Mode) you can select an area of text with the left mouse button, right click on it to copy it to the clipboard and then click the right mouse button again to paste it the current cursor location (reminds me of the good old VT keyboards with the hold key ;-) )