Make a few versions of the same block varying where you place the light, medium and dark fabrics. You will see how the placement affects the final product. Sometimes I make a block and think - ick. So, I've been known to take blocks apart and either change a colour or intensity of the same colour. I am a very far cry from being a natural but have learned that it does get easier.

Try making a couple of small mystery quilts. They force you to work with value - light, medium, dark - contrast. Lots of great learning in them! You can find some mystery quilt patterns right here on this board if you look up paintmejudy and her mystery train rides. Here, I did it for you: https://www.quiltingboard.com/search...archid=3073257

Love your block! So pretty. And the pink center definitely needs to be there. You are a very fine 'piecer'.

Chosing fabrics and colors that work together does get easier and more intuitive with time and experience. But really, there is no wrong way. Just keep making quilts.

Reading the replies reminded me.....

Mock up is just for fabric/color/value placement. So rather than sew a block, I made a paper drawing of the block and made several copies. Then glued the fabric pieces in place. Made enough photo copies to go on design wall. Also made black/white or grey scale copies. Definitely needed some changes.

Also do not forget about basics like crayons for mock-ups! I tend to do more with Electric Quilt, but in my physical notebook with graph paper you can often find colored (either by crayon or pencils) drawings.

I was looking around the internet on pinterest and found this site that sells what is called color cubes for people to use with any color choices that need making. It was very cool to see the end product using their colorways. I didn't keep the link of the site, but I am sure you would find it on the pinterset site.
Oh, google had it on hand. color cubes reviews - Google Search

And this reminded me of a tip from a quilt store owner.

Photocopy your fabric and cut up the copies. Much cheaper than cutting up fabric.

That's a very clever idea, Barbara! I ​​​will def photocopy my fabric for my next mock-up.
​​​​​

Also -: if blocks are going to be joined without sashing between them - to considter the secondary patterns that emerge..

I use my camera extensively. Years ago I had someone in a class tell me to stand back and squint. The camera does the same thing and makes it easy for me to see things that I can't standing 3 foot from my design wall.

My husband is a draftsman. We have a business and over the last 30+ years and have hired a lot of people. He says that visualization ability seems to be something that some people have and others don't. It can be learned but there does seem to be an innate ability to know how things will look. I'm sometimes good at it and sometimes not. I still do a lot of practice blocks to see how things look.