How do you write on a board and it looks professional?

The best answer I can give you is practice. I am a retired elementary teacher and one of the things we did during our training was practice writing on the board. Here's something I did:

https://theapplestreetcottage.blogspot.com/2019/08/the-3-frame-gets-makeover.html

Ok, here are the how to's for painting on wood:

https://www.wikihow.com/Paint-Letters-on-Wood

And here is a source of stencils:

https://www.amazon.com/Stencils-Painting-Cursive-Script-Sayings/dp/B08384L7MP

There are some talented people who can manage this freehand and they are to be admired, hopefully you are one of them, this is a true talent.

For people like me, I need support and structure.

Best to you.

Stenciling is the most professional looking but can be pretty expensive. There are also letter decals you can stick on and less costly. If you are trying to do on chalk board like you are showing picture try using a piece of painters tape to keep letters in line and a piece of cardboard to make straight up and down lines for the downward stokes in the letters.

I learned a trick using stencils that has helped me in the past. After taping the stencil on paint over the lettering part with a clear sealant and let that dry before using a very dry brush to apply the paint.

Hello. I have always found this extremely challenging and difficult. I have found making slight chalk lines with a pastel chalk pencil to be helpful and another consideration might be stencils.

This challenge for uniform printing in a uniform pleasing manner is the reason I bought a Cricut last December.

Here is a link to some stencils, That is what I would use..

Get a Beginner calligraphy book and practice

Hello, I hope this helps you out,

https://smallbusiness.com/manage/lesson-1-mastering-whiteboard-skills-learned-first-grade/

Use a chalk pen and not regular chalk! Game changer!

Are you talking about a chalkboard? I would print out my design using the printer, rub chalk on the back then use a pencil to trace your design. Lift the paper and using chalk trace over your design.