Buy a book from amazon, learn the basics of drawing techniques, try these on paper and on a pc with a drawing tablet. After youve dont the basics maybe buy books showing you move advanced art techniques as learn from there. However if drawing in photoshop i think it would also be gd for your to learn about how to use brushes, such as creating your own, editing existing and also how to use effects and layer styles as this can really help make your image look gd and use less time.