Welcome to Gaia! ::

ooO good question.

i think you need to have a lineart or just even a rough sketch to go on (and you can sketch directly into your program if that's your fancy). a good sketch just helps with an overall composition and i think will strenghten your lineart cause you have reference to go on.

it's good that you're working in a large scale. make sure you zoom into at leat 200-300% when you start to ink. even though it looks pixelated and want to see how the whole image is going.. zooming in will make your lines less wobbly/rough. then when you scale it down.. it looks even more smooth XD

when painting your lineart, i find that bold confident strokes help. my lineart was rough in the begiinning because i was worried i might make a crooked line or something =0=.

good calligraphic line (thin/thick strokes) also help define depth in your artwork too!

and remember... ctrl+z and the eraser are your friends.

hope this helps!

Yuki_Yue makes a very valid point. Sparkle effects -- while it's safe to add them for reference to your sketch -- look better if rendered with other effects.

Also... as to your roughness issue... Try making a truly "rough" sketch of your lineart on a seperate layer (usually in a lighter color -- blue, green, purple, or grey work) and then "inking" over the top with black. That way, instead of using the pen like you're sketching, you're making long, even strokes and curves that cause less variation in line. You might also try making the detail lines thinner than your outline.

Experiment with various brushes and hardnesses... maybe if it isn't looking smooth at a harder setting, it will look smoother with a softer one.

Good luck!