How to prevent smart contract from the vulnerabilities? what are all the security measurements we need to consider before publishing our smart contract?
Vulnerabilities prevention is what you do while coding the contract, i.e. following good practices, like what you can find at https://consensys.github.io/smart-contract-best-practices/
and then, when the coding is done and everything is tested, hiring independent auditors ( not the same people who coded the contract ), those you have to find. There are plenty of companies doing it - check https://solidified.io/ and, naturally, Google search.
Exist some websites with useful information, and of course use correct tools for development.
In the link above you can check best practices and tools and known attacks.