You should read through this to help with the jaggies/clean-up:
http://pixeljoint.com/forum/forum_posts.asp?TID=11299To have it feel more 'solid', you want to define the forms using big clusters of pixels to sculpt out shapes on top of shapes of your little fire man.
I took some anatomical liberties in the design since a well molded design helps rendering be easier without the need of any top technical skills.
For the fire, there is really no easy process. Lots of practice, studying and repetition.
Here is an anim I did a few years back that doesn't really seem like fire at all
Compare that to one that is a bit more fire like from more recent times (though still not very great since it is only a first pass that I don't have time to go over again
)