An early stage investor won't invest in your idea.
They might invest in YOU!
That's more likely if they already know you. Or if your passion is shared or persuasive. Or if you have evidence the market will act the way you predict.
The best way to get that evidence is to "pre sell" your product. This is what people do on Kickstarter. They put their idea out their and promise to make it if people buy. If people like your product and place orders, you get money the money you need to make the product. And you give up no equity to run this experiment.
The number of people who respond, and the amount they pledge are a measure of the evidence that you have already discovered product/market fit. When you actually ship the products you promised, you create evidence that you can actually execute on your plan.
Investors like people who execute, not people who merely ideate.
With that kind of evidence a lot of risk of failure has been removed. That will make it easier to attract investors. As can be seen by the frequent VC offers to companies who have hugely successful Kickstarter campaigns.
If your product is B2B there are similar financing options through markets like KickFurther. And getting LOIs for future purchases is a common strategy when raising money in any kind of business.