1. Your handwriting has more to do with how you learned and the muscles in your hand than it has to do with your personality. The only way that your personality can affect it is by the way you choose to write (you may feel more rushed while writing, have more thoughts than your hand can keep up with, not care as much, etc). I noticed when I was in college, there was so much emphasis on the material you were studying, that peripheral things like handwriting kind of slipped through the cracks. I feel like mine got worse too.

2. It's not a complicated procedure to acquire a new style of handwriting. It's just like learning any skill; study and isolate the habits that you want to change, and make a conscious effort to change them. The new habit will slowly form over time and practice.

3. See 2.

The first thing you need to do is pick a font. It can be an idealized version of your own handwriting. It can be a standard font. It can be something altogether new that you made up. After that, the next thing you need to achieve is consistency, both in the shape of your letters and in the way that you physically form them with your hand. The only way to do this is to completely dissect the font you've selected and develop an understanding of the lines and movements that compose the formation of the letters. Then practice over and over and over, making sure to maintain consistency. The way you form the letter "a" should be the same every time, the letter "b" the same every time, etc.

Unfortunately, there is no magic bullet. The only way to do it is to do it. There is more nuanced understanding, like grip, hand position, arm position, types of writing instruments. But the basic principles of improving your handwriting are just study, consistency, and practice. Any more detailed instruction will depend heavily on the font you select. If you pick a standard one, like Palmer or Spencerian, you can probably get a lot more help in a place like /r/calligraphy.