As a young startup, the things you must avoid include...
Biting off more than you can chew
Protracted timelines/scope creep that can blow out
Over engineering your solution before you know what your users really need
Poor/miscommunication between stakeholders
Over promising and under delivering
This is why MVPs and strong cross functional process is essential.
Reminder: If your problem is getting from A to B then the MVP is a skateboard (then a bicycle, then a motorbike, then a little hatchback, then a sedan, then a Porsche), not 4 wheels.