Some business points that I have compiled from my readings and experience.
Solve people’s problem. Can start with own problem face. A lot of products in the world are result from some frustrations, problems etc of the founder.
Start with what you have. Start with how much you have and can burn, with what technology/tools you know, with who you know. Don’t wait everything perfect to only to start.
Validate with MVP (minimum viable product) or RAT (riskiest assumption tests). Don’t spend everything you have to start. Start small, get real feedback. Are people willing to spend money to buy and use your product?
Economy of scale – a proportionate saving in costs gained by an increased level of production. Specifically referring to manufacturing but also applicable to other industries
Focus on activity that yield the most return/profit/revenue. There are activities that create values, others don’t create any values. It is called waste.
One easy way is to have injected a hidden parameter with a random hash/number (e.g called token). Upon submission you’ll have to check that the token you expect (which you’ll have probably stored in the http session) is being sent together with the other POST parameters. On valid submission you’ll remove/invalidate this token. That way when a POST comes which a non recognised token then it’s most probably a duplicate or out of date request. source
To check whether the data submitted exist in the database. This is the most tedious part to do and you need to have a unique data for this. i.e. the data must be unique in the table or create a unique data for this purpose sent together with other data.
Add a one-time token to your forms and save it to the $_SESSION-variable. Then if it is used (form is submitted), remove it from the session (or create a new token). If the form is then sent again, the two tokens don’t match and you have a duplicate entry (you can ignore the second for example). source