Instructions
Develop an idea for a board game. If you want to be a designer, you need to start by designing your own games. Try a brainstorming session, where you write down ideas, themes and mechanics that interest you, and then go from there.
Write the rules for the game. Since this is an initial part of the development process, don't expect all of these rules to stick. The rules will adapt and change over time, but you need to be able to start play-testing the game, and that takes rules.
Create a prototype of your board game. Take the idea of your polished, finished product sitting on the shelf at Toys 'R Us and throw it out the window. Your first prototype is going to look awful. The point is it gives you a means of playing your game. You can build your first prototype from scratch, or cannibalize parts from the board games you own.
Play-test your game with your friends and family. You need to understand how the game works, if the mechanics are functioning correctly, and if you need to adapt or change the rules. Listen to the feedback from your play-testers, and make any changes that you feel are necessary. Even if you don't think something is an issue, if your entire group of play-testers makes the same comment or suggestion, you should take it seriously.
Create a final prototype. You want to spend a little bit of money on this. Old cereal boxes and a glue stick simply won't due. Make it as professional as possible while maintaining your budget.
Choose between self publication and traditional publication. You can pay a company a fee out of pocket to have your game printed. Then the marketing and selling of your game would be left up to you. If you seek out a traditional publisher, you will need to write a query letter explaining your game, or seek out a publisher at a trade show. If you go the trade show route, bring your prototype and a solid pitch.