@Gameprinter Some very good suggestions there.

I sent an inquiry to a publisher regarding doing something like the Savage Worlds One-shots or one-page dungeons (as a sample I sent my "Crypt of the Witch King" one page dungeon entry) and mentioned that I also did cartography. I've done quite a bit of work for them since. The hardest thing is getting a foot in the door.

Make maps, just for fun and practice. Post them here in the appropriate sub-forum and ask for feedback. You'll be amazed at the quality of help you get and how fast you improve. Partake in the challenges, they get you doing things well outside your comfort zone. Start a finished maps album here - you can use this as your portfolio for prospective clients. Check in the "Commissions" thread and throw your hat in as Redrobes said. Most of all just persevere.