As others have said, highlighting and/or taking notes can be a very useful tool. If you find that these don't work for you, however (as they often don't for me), you can try another tactic: read out loud.
You don't have to speak loudly or do a dramatic reading, or anything, but reading the words out loud forces you to focus on them in sequence (as opposed to just staring at the page as a giant pile of words). Hearing your own voice and feeling your mouth move engages additional senses to the task, bringing more of your attention to the task.
The ideal workflow for reading aloud is to use it to regain lost focus but to resume reading silently once you're concentrating again. Unless you are a slow reader or a very fast talker, odds are good that you can process information faster than you can pronounce the words. Use reading aloud as a technique to distract yourself from the distractions, and then get back to work.