Research is a capricious mistress. You should be totally devoted to it, and you should be thinking about it all the time. Otherwise, it won't divulge its secrets to you.
Research has this nonlinear return on investment (ROI) function. It awards persistence and dedication by folds and punishes apathy and laziness severely.
If you give research your 100%, you will get at least 200% ROI back. Eventually, that is. It will first test you to see if you are worthy, if you really mean it, if you really have it in you. You will get several setbacks, false alarms. Yet, if you persist and overcome the failures, it will start giving back to you by folds.
If you give research your 50% you will get 20% back. You won't make the cut, and you will be operating a business with deficiency. Usually someone else (the university that employs you) pays the tab.
So what does giving 100% mean? It doesn't mean working overtime (sometimes that will be needed, and you will be doing it though). The productive focused working time (i.e., deep thinking time) is limited to 4 hours a day more or less. There seems to be a bound after which your brain refuses to make progress; it is as if your brain needs to wait to adjust for and catch up to what it had produced. It won't go further even if you push more. I liken this to climbing a mountain; you have to rest daily to let your metabolism adjust. (This 4 hour bound has been anectodally mentioned by many researchers, but I don't know of any detailed analysis of this. For example, I don't know if it is possible to fit in 8 concentrated hours as 4+4 on two different projects. I haven't been able to succeed so far.)
Let's stick with that 4 hours daily. Are you giving that focused 4 hours to your research? Only a small fraction of researchers can answer this affirmatively. How can you cultivate this deep thought? It is hard work. Be persistent and try different things until you find what works best for you. Here are some necessary conditions to get you started. First, turn all distractions off. Don't check your email, twitter, browser in those precious hours. Go offline if possible. Secondly, you should be writing and taking notes. You need to be writing to be able to think in a concentrated manner. If you work with pen and paper (or a whiteboard), you can get more visual, you can doodle, you can link concepts. If you use a good word editor (I swear by Emacs orgmode) and keep typing as you work, the bonus is that this often will be your zeroth draft for your research paper, and you won't get stuck in thinking how/where to start writing.
After paying your dues to your research in those 4 hours, you are still not off the hook. What you should do is you should think about your research in that remaining time. This is the digestion and cudding process. At the background of your brain, you should revisit your research at different times of the day. You do this to see 1) if what you produced holds water, and 2) if by approaching from different angles you can make more progress. You come back to your research again and again during the day (while driving, in the shower) to see if you can catch your research off-guard and get more secrets out. But, you should not let this thinking/reconsidering turn to worrying. Worrying is unproductive and harmful.
If you make some progress regularly and persistently, you will get to see the many folds return on your investment.