Play lots of games, both good and bad, modern and classic. Take them apart and figure out what makes them work and what's wrong with them too. Be able to articulate this so you can use the information when you tackle your own designs.
Once you're ready, strive to do something different and intriguing. Figure out how to learn from your failures and to design around them. Be dedicated to improving your work at every stage.
If this is something you really want to do, don't give up. It's not for everyone, of course, but even legendary designers have publishers reject their games. You need to be able to dust yourself off and jump back in again, without rage or ego but with determination and a love for your craft.
Love this answer Matt. Your mention about determination and love for your craft is applicable in different settings. Thanks for sharing.