Start scribbling! Your first map most likely won't be what you want. Neither will your second. Probably not your third. Draw a few spirals. Draw some star fields. Do a whole bunch of basic tutorials for the tools that you intend to use, be they pencil and paper or some sort of software package.

Making a pretty map is hard. It takes practice. You'll need to learn to use the tools and you'll need to learn get things in pleasing places. All of that takes time and practice. Lots and lots of practice.

Don't be a perfectionist. Don't be afraid to make mistakes. One of the fastest ways to get better is to post your work-in-progress here or somewhere that is doing the sort of things that you want to do. People want to help and some of them will probably even be helpful.

Above all, don't get discouraged. Getting good at anything takes time and practice. Lord knows I've spent a huge amount of money over the years trying to find the magic box of software that has talent in it. Mostly what I've learned from that is that nothing beats an artists's vision and practiced hand.

And a final word of advice: get started at doing something now (and repeat until you get close enough to what you want to make yourself happy).