*CLAPS LOUDLY* THANK YOU NOW I REALISE WHY SO MANY PEOPLE LIKE IT BECAUSE THE LINES ARE ALL PERFECT
To answer your question, I learned to draw by directly referencing pokemon books and the pictures of the pokemon, then drew them in the same pose. It was great fun as a kid and I just did it enough I had an arsenal of abilities to draw curves and straight and stuff.
I drew this with a slight reference, first time in a while with any reference.
Otherwise I dunno man. Practice and time.
The hard way done in probably not even the most efficient manner I started at ~5 and I'm 15 now.