More options for managing node display
In general, as Clive said it is difficult to give answer to a question that broad in scope. But in general there are two broad directions:


Use Modules like Panels and Display Suite - These allows customizations in node pages by allowing you to chnage layout, add different contents etc.
Follow custom theaming path. this involves writing modifying the preprocess function and modifying the node.tpl.php


Any more specific info will require you to give out more details in terms of what you want exact in terms of layout and "clean up"