hey AlfonsoX ino you want to get better dude so im not gonna sugar coat this
first off you not varying your mark making using the same brush EVEryWherE! this makes your images muddy alos your values are too close together combine that with bad edges makes it worse!
you need to work on your drawing and values i suggest hitting the loomis books, all 6 of them are free pdfs online google dat shit.
for value check out my sketchbook follow the value study form scot robertsons mate suface rendering dvds
as for the brushwork read this paintover tut i made for razvanb08
http://crimsondaggers.com/forum/thread-858-page-7.html
use a soft airbrush for soft forms and a noraml hardround for edges
soft brushes for soft things
hard brushes for hard things
easy right :)
tiny color theory tip
http://crimsondaggers.com/forum/attachment.php?aid=9197
when your lighting or darkening colors,form,light whatever
be mindfull of color temperature
rule of thumb is Warm light=cool shadow and vise versa
you can the the light tempreture by simply the color of the hightlight and areas of mass-light which way dose it lean to warm or cool?
in the the original above raz went too warm with the shadows and lights her skin is quite pale but theres tonnnes of colors , theres greens and pinks in the areas of mass light and blues purples and green blues in the shadows but if you color pick them they just look like normal skintones?!?!
thats because colors are relative the tempreature refers to in which direction of the color wheel the hue is shifted, cool grey shifted a bit to the green on skin looks like blue vein but it isnt blue its just a cool grey...ITS WHATS AROUND IT that makes it look like a cool grey ...weird shit right
a neutal gray would look redish in a sea of blue
work on your drawing , also quick tip dont "pet" your lines be confident and do whole strokes thats one way to get better edges
best of luck man n happy painting :D