I am using twitter bootstrap and i need to change the basic visuals of the framework like the form element etc. Is it a good practice to over write all the styles again in styles.css or modify the bootstrap.css and change the styles directly.
Is there any tutorial which teaches how to set up LESS for Bootstrap and use it ?
See Twitter Bootstrap Customization Best Practices regarding customization and LESS with Twitter Bootstrap.
In general, I wouldn’t recommend directly modifying your bootstrap.css file, because it will make it difficult to edit in the future if/when the core css is updated by the bootstrap folks. Instead, just have a second style sheet that is referenced after the bootstrap css. Add your overrides/modifications there, like so:
Of course, for performance, consider combining these and serving them as one to reduce your http requests.