Start out with a plan, and spend as little time as you can in the prototype/experiment stage. Write down what you need to do to create a "minimum viable product".
A minimum viable product model is what all "coded in X hours" web-apps create. Quite literally, just launch as soon as physically possible; if you expect not-required-but-cool-feature-1 to take an extra 2 hours to create, and you really think would add quality to the product without adding unnecessary bulk, then just add it to the 'post-launch to-do list'. You have a massive advantage creating a web-app — the ability to instantly add features after 'launch'. Don't waste it!
And to help with creating a minimum viable product, always do Test Driven Development. While this actually adds to the amount of code you have to write, generally you will get the app finished quicker, or at the very least, it'll help you stay on track.
Start out with a plan, and spend as little time as you can in the prototype/experiment stage. Write down what you need to do to create a "minimum viable product".
A minimum viable product model is what all "coded in X hours" web-apps create. Quite literally, just launch as soon as physically possible; if you expect not-required-but-cool-feature-1 to take an extra 2 hours to create, and you really think would add quality to the product without adding unnecessary bulk, then just add it to the 'post-launch to-do list'. You have a massive advantage creating a web-app — the ability to instantly add features after 'launch'. Don't waste it!
And to help with creating a minimum viable product, always do Test Driven Development. While this actually adds to the amount of code you have to write, generally you will get the app finished quicker, or at the very least, it'll help you stay on track.