One of the tried and true methods for finding a winning idea boils down to finding a common problem and providing or building a solution for it.
Step 1: Find a specific demographic of people/businesses. (Ex: Accounting Firms in Chicago, Sushi Restaurants in California, Small Advertising Firms in Nebraska).
Step 2: Conduct 20-50-100 short interviews with willing people who fall within that demographic. Ask them a standard set of questions involving their day-to-day operations, their challenges, their roadblock/bottlenecks etc.
Step 3: Ask if they'd be open to you coming back to them a few weeks with some ideas on saving time/money or solving those problems.
Step 4: Find the most common problems, and decide on one, or a small subset of them to tackle. Optimize a solution, then return to those people you've interviewed with a proposed solution.
Step 5: Give them a timeline for when you can have a first demo/MVP (minimum viable product) by. Once you have this, have them commit to 3 months of your service and see how it goes.
Step 6: Prepare the roll-out, and build out full functionality now that you have the money to do it with.