Being a serial entrepreneur I have observed that start-ups can easily become a failure if one does not take care of certain measures from time to time. Here are some of the major things one should do to make their start-up sustain:
Know your audience. Specifically target a well-defined group while designing your marketing strategy
Set aside the larger portion of your investment budget for marketing (either conventional or digital marketing)
Focus on word of mouth approach. Try to use your personal contacts to build good credibility of your product
Maintain prompt customer service, it works like a wonder!
And most importantly one should stay super-motivated and optimistic about keeping up with the ups and downs of the start-up