Just some of highlights from Paul Graham's post with same title.
-- Quote --
The mistake they make is to underestimate the power of compound growth.
Marketplaces are so hard to get rolling that you should expect to take heroic measures at first.
Almost all startups are fragile initially.
The big danger is that you'll dismiss your startup yourself.
Get some initial set of users by doing a comparatively untargeted launch, and then to observe which kind seem most enthusiastic, and seek out more like them.
It's not the product that should be insanely great, but the experience of being your user.
By building something you yourself need, the first thing you build is never quite right.
It's often better not to aim for perfection initially.
Sometimes the right unscalable trick is to focus on a deliberately narrow market.
Any startup that could be described as a marketplace usually has to start in a subset of the market, but this can work for other startups as well. It's always worth asking if there's a subset of the market in which you can get a critical mass of users quickly.
Among companies, the best early adopters are usually other startups.
B2B startups now have an instant market of hundreds of other startups ready at hand.
Sometimes we advise founders of B2B startups to take over-engagement to an extreme, and to pick a single user and act as if they were consultants building something just for that one user.
When you only have a small number of users, you can sometimes get away with doing by hand things that you plan to automate later. This lets you launch faster, and when you do finally automate yourself out of the loop, you'll know exactly what to build because you'll have muscle memory from doing it yourself.
Some startups could be entirely manual at first. If you can find someone with a problem that needs solving and you can solve it manually, go ahead and do that for as long as you can, and then gradually automate the bottlenecks.
It's not enough just to do something extraordinary initially. You have to make an extraordinary effort initially.