Instead of drawing in Gimp/Photoshop, etc.
I used a couple of websites quickly and they seem really good at
either pen control or line smoothing/tapering.
If you don't have good software (Gimp is a good free software you can use though)
then try a one of these websites:
(They seem safe and stuff but whatever)
http://artpad.art.com/artpad/painter/
Quickly drew:

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https://sketch.io/sketchpad/
Quickly drew FF fan game concept art:

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*Draws Venom from Spider-Man. Says it's FF concept art*

Cartoon Network Universe, X, not Marvel Universe.  

yeah I'd feel terrible if I tried to draw a dog and then someone came and said it was a cat.   

though this is X so who knows.