Good hand writing does leave a good impression but bad hand writing doesn't leave an bad impression as long as things are vivid and well managed. I have friend 21st Poisition DMG 2009 as an example, his hand writing is made only for him to read, yet he managed to secure such position.

Here are two tips for you!
1: Find out our best words or alphabets: that could be anything, like of, to, that, this, the etc. try to write them with ease and elegance.

2: Find out your worst words or alphabets: try to write them with ease as well to get best out of them.

Rest is all practice.
Best of Luck!

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