Just start typing and hit one of the Title Stiles or make a New Style.
I just found this on another site and it works:
you can create a template with the text set to what font/size/colour etc. that you need. To do this just create a title and change to your desired settings, then delete the text.
Select the "templates" icon near the top left of the title designer window, select "templates" from the title menu or hit the shortcut "Ctrl+j".
Select the little triangle/arrow icon at the top right of the templates window and select "Import current title as template" from the drop down menu.
Select the same little triangle/arrow again and select "Set template as default still" from the drop down menu.
Now when you create a new title it will open the title designer with the settings you chose.
I had asked this before and got the usual "use a template or select a style" and in my head I'd never got around how this could be useful when having to change hundreds of text sheets set up on somone elses project passed to me to work on - and my ddefault was not the same as theirs.
Having done this - its soooo easy -- thank you!
This question should be marked as "answered." johatk86's answer is correct.
If you came here in 2020 or later like I am, just an update this doesn't work/isn't an option anymore. Apparently you have to set a master style and then select it every time you go into a project. And master styles don't transfer between projects for me so... Adobe a default text would be great.
Truly mind boggling something as simple as a default font (or even just remembering the last one you used) should be so hard... but then again this is how Adobe does.