After getting a graphics tablet, my workflow really improved when using software like Photoshop and Illustrator. It meant I could draft and sketch out my initial idea and then go over it using digital software.
Here are some examples:
This is a fan made t-shirt I did for the band Megadeth.
And here is a play on words of a song Master of Puppets by the band Metallica.
Here I created a small cityscape of a sci-fi dystopian city by using basic single point perspective and some light shading.