For me, I find it easier to do something that I personally want. I am a user that I know well. I have accurate data on what I actually spend money on. I can identify people like me. This sequence is a good seed. I know all the places my money goes, so go to those places and ask people who are there.

If you make something that you like, but other people (similar to you) don't like - don't pursue that.

If you make something that you like, and others like you also like it and want to give you money for it, then go go go.

I made http://traxda.com because I wanted a 3" lift kit and not a 6" lift kit. 10 years later, so have 120,000 other people. (found people at auto related places)
I made http://sascase.com because I wanted to protect my Ipad from my kids. 3 years later, so have 3000 other people. (everyone has a phone, did nothing but have the case on mine)

I once bought 27 truck loads (48 foot trailers) of old man truck accessories. $2,000,000 worth of product for $150,000. The only problem is that it was product that I would never, ever, ever, buy. So while the values were correct, and I sold a lot of it ($1M before I gave up, net loss of money -150K), it was a market that I didn't understand, I didn't like and I did not know enough to even ask the right questions. It was a huge disaster, one that lasted 5 years before I gave up. Lost time was worse than the lost money. Stupid stupid stupid of me. I got the basic business equation right, but I did not get the subtle details and this is what caused the loss. If the product had been something I cared about, I would have known these little details.

I had a friend talking about making an app for elderly people who need to take meds. He is 25, and nobody he knows fits this description. He was convinced it would be great, there are all these news stories about people getting older, blah blah blah. I asked him if he would still be interested in his app in 10 years, because you end up doing these things WAY longer than you think you will. He told me he was going to growth hack it and flip it to Google in 2 years (he has no contacts at that, nor experience). It took a while, but I convinced him to drop the idea and focus on something he would pay money for. So he did, and he tells me hi is much happier.

If you are talking to potential customers, and they verbally tell you that they would buy - why not ask for a deposit? or a pre-pay?. It is the old school, personal version of crowdfunding. How things were done before Kickstarter. I used that trick to get $5000 together for a buy in to a hardware wholesaler in 2000 (and then learned I hated selling nuts and bolts despite the 50% profit margin. Boring). Don't be fooled by people who SAY that they will buy, but won't get out their wallet. Read Predictably Irrational by Dan Ariely http://danariely.com/2009/08/10/the-nuances-of-the-free-expe...

My next project is some software I need for running a small manufacturing business. Nothing I have looked at in the last 10 years has been appealing (too complex) so I am making my own. I don't know how to program , but I do know I would write a check for thousands of dollars today if someone walked in the front door with the solution I have in my head. I know the problem well, since I have been dealing with it for 10 years.

So ask yourself - what areas do I know well? What do i ACTUALLY spend money on (instead of "I think people not like me would buy this"). What product if it existed would I reach for my wallet RIGHT NOW to buy?