As a scientist, your are expected to be at the boundary of the current knowledge in your field. You should know which state-of-the-art methods are used. The newest findings should be know to you. And more importantly, you should know what is still unknown.
As a PhD candidate, you are learning to become a self-sustainable researcher. Therefore, a PhD candidate should, in the end, be at the boundary of the current knowledge of his subject and maintain that knowledge. So how do you keep up with the fast expanding frontier of knowledge in your field?
My trick to stay at the boundary of the current knowledge is to keep an eye on the most important journals in my field. You can do this even if you are not subscribed to the journals. Every journal has an RSS feed (I know this is an ancient tool, but it works so why don't use it), that gives information on the latest publications of the journal. Most of the cases, it releases the abstracts of the latest accepted articles.
Journal of Geophysical Research: RSS-feed for example
Just look for RSS-feed on the home page of the journal.
If you link these RSS feeds to your email, you will be posted when new articles are available. A quick look in the titles and abstract texts of the new journal papers should give you an idea about the relevance of the article. So open your email to the frontier of knowledge!
PS. cool link about this subject. It keeps you humble!