I have a few notebooks full of ideas. Detailed ideas.
I usually take a look and decide what would be the most interesting for me to work on at the time. I figure if I am interested, I'll stay motivated and therefore have a better chance of completion.
I would say expose them to the light of day, have people critique them. If you are really self aware try to match your skills to what the implementation to each idea requires.
Easier way ( shameless plug follows) I am part of a team to crowdsource such work or atleast the customer development and feedback part for now.
Going live on Feb 8 th. Check out www.crowdraising.co
Not .com
I like Musk's take: "work on the most important thing".[0]
If money is enough to drive you, try to find out which is more profitable should do it, but being useful and good to people and mankind in general is an added bonus and motivation.
Make a pitch for 3 of your ideas that you think have the potential to make the most money. Pitch them to your friends/colleagues/people whose opinion you trust who would be in the market for such a product.
Ask them which one you think is best/most likely to be a product they would use. Tell them it's okay to say none of them. If no one thinks those 3 are good move on to the next.
I usually take a look and decide what would be the most interesting for me to work on at the time. I figure if I am interested, I'll stay motivated and therefore have a better chance of completion.