Everyone says to pre-sell before you build. Most fail to do so because they've never had a plan to help them. Treat it like a science experiment by following the Rule of 100 to determine if your project is worth building.
Decide your ideal customer
Compile 100 of those contacts
Set a goal for success. If 10 buy, will I build the thing? If I can't find 10, will I move on from this idea?
"More bootstrappers would succeed if they focussed on sales rather than marketing." - Courtland Allen, Indiehackers
These questions are necessary to determine if your target market exists. If so, how can we repeatedly find them? And how do we message them about the benefits they could experience by working with us?
Example: It's a tried and true method of aligning your capabilities with your customer's needs. Let's give it a try for Eamon Keane's Project Rina, a Twitter Publishing Tool.