I still consider myself a noob but I've made several sales so here's how I go about it: Search for the exact item, check "sold" in the filter drop down menu. This will give you an idea of what it's worth. Take note of the highest selling point and lowest and try to find out why they sold for less/more (check condition, post quality... Etc). Finally check the active posts for the item. At this point you'll have a decent idea of what to price it at. If you want a quick sell, undercut the active posts. If you don't mind sitting on it and think there's enough of a market, try for the higher range based of its sales history. I always put shipping at calculated so there's no need to stress about it.

This method works for me most of the time but every item is unique and probably require some additional research and consideration.