If you are starting over from scratch and don't have much expertise in what you are dooing, targeting keywords in the range from 1000 to 10.000 searches per month would be a perfect way to start imho.
If the competition isn't of high quality, you can start to rank soon enough so that you don't lose your motivation. If your sites rank and you botch it (like buying the wrong link package and getting your site penalized by google) it's not such a big deal. You can start over again.
When I started I targeted keywords around 2.000 to 20.000 in search volume.
Actually all of this differs from niche to niche and how you want to make money. If you want to sell a product for 8000$ and your share is 800$ even a low search volume of 100 might be attractive to target. If you want to make money based on leads for a free service that gets you 2 $ per signup, you should target much higher search volumes. It really depends
Hope this helps you a bit. If you hand out further information about your project and financial goals (e.g. if you live somewhere in the third world and 100$ are a big amount of money to you, there are LOADS of niches that are not heavily marketed by other IM guys)