Well I'm not yet an experienced developer but I would write here what I have seen in experienced developers at our company.
Our company background
We are a small team of 7 developers. One software architect, two senior developers and four junior developers. We primarily work on an ERP Qbil Trade in PHP Symfony framework, AngularJS, Prototype.js, etc.
The most inspiring characteristics which I have seen in our senior developers is that they try to write future proof code as much as possible and they try to make reusable components which are then used again and again without repeating the code though we use an MVC framework still they develop custom controllers, functions and actions on top of that framework most of them being generic.
Now whenever our clients ask for some modification or some feature request, mostly everyone of us knows where to start from and what to do because mostly the base for almost every new feature or modification is already set.