[simne]

Most time consuming and most important in startup is gather first time clients, so use any possible things to got clients for free (or semi-free, for example on venture events, or become part of some platform, like consoles in gamedev) or to just buy leads traffic for example as pay per click.

All other things are very different, very specific for each startup, and depend on what is your target environment, what is your kernel tech, etc.