[usedtolurk]

It's hard to answer that question because so much depends on your specific circumstances but I'll try. I'm assuming you're able to do your own programming because $1000 won't get you very far if you need to hire developers.

Find an area where you think you can provide something of value. It could be a hobby or a problem in your community. Figure out how to solve it and have a go. Get feedback early and keep an open mind try lots of things and understand what's working and why.

If you don't already know patio11's Bingo Card Creator story, then probably the best advice you will find is on his website:

http://www.kalzumeus.com/

Read the earlier ones on how to prioritize your time and validate your work (the more recent posts are more geared towards SEO and marketing).

Also Eric Rees's blog about the Minimal Viable Product approach: http://www.startuplessonslearned.com/

But you've been on HN for a while, so you probably already know all that?