How can I train myself to build better software?

What is your approach to build an efficient Java application (with/without pre-existing legacy code)? I am more curious to know how you design the whole thing so that loosely coupled, easy to manage, pluggable components can be developed?

Consider this app will be used for following purposes - a) To push data to JMS queues b) To query data from database/cache c) Verify against some expected result (from a CSV or Excel or text) d) There can be a web frontend of the app e) The app modul...