I hate to be the bad guy, but if you have to ask where to invest it in advertising then you're probably not going to make a positive return on investment.
There's quite a learning curve to paid advertising, generally people start in PPC by learning how to track keywords, conversions and split testing landing pages.
Depending on what kind of advertising you're interested in, if it's PPC then I suggest reading as much as you can, set up tracking and invest a small amount of money and start learning that way.
On the other hand there are firms you can pay to run your PPC campaigns, I have no experience with them but I've seen that they usually start with a $10,000 investment.