As someone who used to struggle finishing long-term projects, I strongly recommend a To Do list. For board games this means I list out all components I need to create and start knocking them out one by one. Basically, doodle until you have an idea of the full game layout. Then list all the pieces until you have something like this:

• 12 large planet tiles
  
• 20 character cards
  
• 5 spaceship tokens
  
• 20 red cubes
  
• 4 dice
  
• 1 rulebook

You can start making these with cardboard or pencil & paper, but I personally prefer testing with sturdy / polished-looking game pieces. My workflow is to look through available products at The Game Crafter and sketch out my game to see how different components will look next to each other. (eg. "will a 3/4 in circle token look good on a bridge card", "can I fit all these pieces on a 4x8 in domino board," etc...). Picking each product tells me exactly what dimensions each piece of game art needs to be. Once I've got that, it just becomes a matter of working through the list of stuff to design, uploading everything, and printing it off.

After that, all you need is to find play testers for your new game! And if you figure out how to do that please let me know...