Here are instructions for setting up the defaults the way some people have found helpful:

1. Open yEd.
2. Create a new document.
3. Click the white background; a small yellow square should appear on the canvas.
4. Click the small yellow square so as to select it.
5. Click and drag one of the corners of the yellow square to resize it. Make it the default size you'd like your text boxes to be. You will be able to change this later.
6. Make sure the yellow square is still selected.
7. Look at the menu in the lower right. It is called "Properties View". It will show you information about the yellow square.
8. Click the small yellow square in the menu next to the words "Fill Color".
9. Select the color white for the Fill Color.
10. Lower in the menu, under "Label", there is an item called "Placement". Find it. Change Placement to "Internal" and "Center".
11. Right below Placement in the menu is "Size". Find it. Change Size to "Fit Node Width".
12. Right below Size is "Configuration". Find it. Change Configuration to "Cropping".
13. Right below Configuration is "Alignment". Find it. Ensure that Alignment is "Center".
14. In the upper toolbar, click "File" then "Preferences".
15. A menu will come up. Click the "Editor" tab.
16. You will see a list of checkboxes. "Edit Label on Create Node" will be unchecked. Check it.
17. Click Apply.
18. In the upper toolbar, click "Edit" then "Manage Palette".
19. A menu will come up. In the upper left there will be a button called "New Section". Click it.
20. Name the new section after yourself.
21. Verify that the new section has been created by locating it in the righthand list of "Displayed Palette Selections".
22. Close the Palette Manager menu.
23. Doubleclick your white textbox to edit its label.
24. Put in something suitably generic to indicate a default textbox. I use "[text]" (without the quotes).
25. Select your white textbox. Be sure that you have selected it, but are not now editing the label.
26. Right click the white textbox. A menu will appear.
27. On the menu, mouse over "Add to Palette", then select the palette you named after yourself.
28. On the righthand side of the screen, there will be a menu at the top called "Palette". Find it.
29. Scroll through the palettes in the Palette menu until you find the palette you named after yourself. Expand it.
30. You will see your white textbox in the palette you have named after yourself. Click it to select it.
31. Right click the white textbox in the palette. Select "Use as Default".
32. To check that you have done everything properly, click on the white background canvas. Did it create a white textbox like your original, and then automatically allow you to edit the label? If so, you're done.

Then... a. Click the white background to create a box. b. Click a box and drag to create an arrow. c. Click an already existing box to select it. Once selected, click and drag to move it. d. Doubleclick an already existing box to edit its label.

Enjoy!

There's a few settings you should tweak at the beginning

Deets? I use yEd all the time, but I've never made any tweaks.