The Creative Economy: How can I become a successful board game designer?

You've picked a great time to be a board game designer.

According to Wizards of the Coast, last year's Gencon was all board games

Dungeons & Dragons is booming online, but not in the way you think

There has been a return to conventional board gaming from computer graming for the very reason I never left it - the social side. You get together with a bunch of friends and enjoy an evening's interaction. Computer games just don't give the same experience yet.

So this means that there is an ever growing number of people ravenous for board games.

And there are more board games than ever.

Are you a one-hit wonder? Do you have a great idea for a board game or do you want to be create more than one? That's an important question because it will influence how you approach this problem.
Start with what you love. There looks like a lot of competition but there isn't because keen "Monopoly" players are not that interested in "Trivial Pursuit" or "Rail Baron" and vice versa. So start with the games you love. I demand that a game should have everything in it needed to win and so that it can be won by anyone playing it. This is why I hate "Trivial Pursuit" because it depends on a large wealth of general knowledge and so is prejudiced against children. I see that there's finally a kid's version so that they now have a chance.
Treat it as fun. If you're not having fun, how will others?
Look at Variations. Pick an existing game and take it new directions. For example, "Kill Dr Lucky" is the flipside to "Cluedo". In "Cluedo", you try to work out who the murderer is, in "Kill Dr Lucky", you try to become the murderer.
Simple design. You need a game that can be easily learned but that can also be played again and again. So you need both simplicity and complexity. The complexity can come from randomness (thus the use of dice and cards) and/or by expansion packs. Or both.
Protoype. Make a physical version of the game and play it.
Go to Kickstarter etc and see what's out there and what's been successful in raising its crowdsourcing targets. Are any similar to your game? Do you get any new ideas about additional features you can add to your game?