for cubes, I start counting from the bottom and work my way to the top.
With enough practice, you can do this pretty fast and pick out the individual cubes. You just have to get used to 1sided cube, 2 sided, 3 sided, etc.
For TFE, I would be careful for counting lines. It's a great way to start but on the real DAT, chances are all of the answer choices will have the same number of lines which means it's really difficult to tell the choices apart.
Practice visualizing the 2D object in 3D, it's not the easiest but with practice you'll see it eventually, but for easy ones, yes you can just go ahead and count the lines and move on.
Good luck