Conducting an online job search is somewhat like looking for a needle in a hay stack. You have to always keep in mind that the www is a giant world-wide library with no card catalog. Search engines that pre-sort results and topical search tools can help to a degree. But in the end your success will depend on your persistance.
I find that the key to successful job searches using the internet really start with effective uses of key words. Make sure you know what the current job titles are within a field and commonly used phrases within vacancy announcements. Job titles vary between geographic regions. If you are a recent graduate, be aware that terminology within a specific resource occupation may be older than your knowledge.
Talk to currently employed resources staff and discuss how they word their job announcements for advertisement. This may help you narrow your search objectives. Study job postings and start a list of 'key words' or phrases that seem to show up regularly. Try different combinations of words, and different word orders. Search 'engines' can give you different results simply by changing the word order. Current politics of an environmental subject can influence how job announcements might be advertised between regions. If you are getting a million results your word choice is too broad. If you get 2 or 3 link results for a search then your word choices are too restrictive. It takes some trial and error to find the 'right' search word choices.
Remember, not only are you looking for a job, htere's also an employer looking for you. Keep searching!