You have several workflow, but it’s always depending of your needs, or what you are more confident with.
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Photoshop, or other 2D programs (don’t know Krita very well
)
I assume it’s very depedant of your drawing skills and the brushes you are using.
And you have all the filter available, like blur, distort, etc… You can see some tricks here : Question About creating VFX textures! -
Substance Designer
If you are confident with node programs, this help to do very easily seemless textures, and procedurally ones. You can also make simple mathematics shapes, or import custom texture and add some noise and grunge pretty simply. -
After Effect
I’m not using it that much, but I saw a lot of tutorial that help create fluids textures and little flipbook, and combined with a plugin called ‘Particular’ you can making very cool stuff ! -
Houdini
That’s the one I am using the most, for realistic smoke flipbooks for example (you can do a lot of other things, obviously, and not necessary realistic). You can also use fume fx or other programs like that, but it’s need a lot more technical skills to achieve the shape you want.
And this very cool site, for very common texture, if you are lazy like me 
http://mebiusbox.github.io/contents/EffectTextureMaker/
I assume there is a lot more way, but this is all I have in mind for now, maybe other people will complete this !