First spacing- I would model to the student how to write one sentence with exaggerated spacing. Then have him copy just one sentence. Then ask him to write another sentence using this exaggerated spacing just to get the idea.
On the click/away site that you can register (in the inside cover page of any Teacher Guide. www.hwtears.com/click there is a page that addresses this issue.
Next, I would work on only the letters that are difficult to decipher and to work on those letters, you can use list copying such as on page 66 of the 2nd grade teacher guide. It is very difficult to correct any poor habits (such as starting from the bottom) for an older student. I would just work on the legibility (the control of the pencil)
Letter size- you can try to use the hand sign activity - just for fun. Maybe use the reading word or spelling word list – just to emphasize the different sizes
Letter placement- Using our double lined paper for a short while seems to help get these students back on track with both the letter size and placement. In addition, demonstrating to the student how to write on the various lined paper that they encounter in class is important.
The most effective idea I had with a high school student who was not motivated at all to write legibly was the following. In NJ, the driver’s permit to obtain a license must be handwritten. I had him practice writing legibly, so that he could complete the application. This activity was the only thing that he was motivated to write correctly.