I was unpleasantly surprised to find out that there are so few Photoshop tutorials on how to create realistic looking sketch effect or pencil drawings. To create a sketch from scratch is not an easy thing to do, you need real drawing skills. So Photoshop has a lot of sketch filters to help you create that pencil sketch effect. But as I found out you have to do more than adding one sketch filter like graphic pen or conte crayon for example. You have to combine several filters with textures and brushes.
Anyway here are the best sketch tutorials around the internet that teaches you how to create a sketch in Photoshop; and some of these tuts are really professional so check them out.