Did you use some sort of line tools? The lines are different from your past pictures.

And I noticed the lower half of Sparks' body has thinner/unclear lines, do you have problems on that or intended to create some sort of effects?

I used the Photoshop basic brush for the whole thing.

It might be because of the pressure I used on the lower half of the body. I might just be impatient since I get interrupted often during my drawings.

SAI has few tools that are ready to use, by tweaking the parameters, it is very good for beginner.
But Photoshop brushes are require to tweak/know a lot to get the right settings (tat's why I stuck with SAI first ^_^;).

Well, beside drawing skills, you might want to have a set of good attitudes/mind set as well. It could affect the outcome of drawings.
Do not be afraid if you cannot finish it on time. If you think this piece's quality is more important than time to submit, just spent few more times on it. Having good practices will help as well, such as trying to use same brush thickness/pen pressure over a certain area, even you get interrupted/after a short rest, you can catch up with it. Since you already get used to the settings.

You can do it Sparks!
I believe!

Glad you still believe in me ^^

Hang in there, you can do it.

I know Sparks can do it!

Say hello to your big friend, Sparks!