Writing neatly is a important skill but it will not come automatically. Writing neat takes practice and time, but with that even a older adult can learn how to write better and neater.
Sit up straight and avoid slouching over the paper while you write. Slouching will cause handwriting to be uneven and become messy. This may take a little practice if you are use to slouching while writing, if you are slouching to much you may to evaluate your need for glasses.
If you are having trouble with maintaining neat handwriting consider changing up your grip. There is many ways to grip a pencil. The point in gripping the pencil or pen is that it his held to be able to control your writing in a sufficient matter. Some ague that there is a wrong way and a right way to hold a pencil, but as long as you get your desired outcome I do not see that there is one set way to grip a pencil.
One of the easiest way to turn messy handwriting in to neat handwriting is to get a handle on the height of your letter. Try to be consistent on how high you letter are and avoid having letters are ranging to far apart in size.
It is hard on the eye to read handwriting that has inconsistent spacing. If someone has to guess where a word start and begins they are going to preserve the handwriting as messy. The same goes for handwriting that has so many spaces between them that you could fit small words between them.
Neat handwriting will touch the base of the same line in a constant manner. To keep handwriting neat make a conscious act to not float letters above the baseline and start letters at the same point of the paper.
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