Techniques for Diagrams with Clarity (less fuzzy)

[bobbywest87]

I've consistently had an issue with all my diagrams turning out fuzzy/grainy. I'm pretty sure it's because I'm using too many colors, but I've seen other user's diagrams with tons of clarity and sharpness.

Can someone with experience provide some advice on how to create clearer (sharper) looking diagrams?

For example,

Here is my before/after:

Before shrinking to appropriate pixel size:


And after. Notice it appears pixelated and out of focus:




I am trying to work towards diagrams with lots of Clarity AND Detail such as this one below from Steamboy (obviously he is/was a much more talented artist, but that's besides the point):





Any advice on how to make my drawings less fuzzy/blurry?