Sleep.  Seriously.  Also, "downtime".  During both of which you integrate short term memory into long term memory. and also form associations that you can't consciously control.<p>I find that when I'm rested, I can maintain several more items in my working memory.  It also frees up your working memory to take on new items, with the previous material now ensconced in long term memory.<p>Health.  If you are feeling poorly, it's going to be distracting.  Also, exercise is increasingly shown to have a large positive effect upon mental function.<p>Eliminating negative distractions -- even those you may be unaware of.  Anecdote:  Back in college days, a friend pursuing a chemistry major used to study with music on.  One time, he deliberately avoided the music -- perhaps I or someone convinced him to give it a try -- while studying for the next exam.  He did significantly better in the exam, by his own evaluation, and was quite surprised by this.<p>I'm not saying everyone reacts the same way to music; rather, you need to be aware of your own, personal reactions.  And sometimes this is not obvious.<p>I've reluctantly begun taking a low dose of Adderall, recently -- partly in response to some chronic health problems that I won't go into.  It helps a bit in some ways, but also hinders me in others.  It does NOT produce the deep, rapid, and highly insightful quasi-fugue / focus state that I could get into -- with some effort -- when I was younger and particularly in better health.<p>Perhaps some of the newer nootropics are better -- they are quite expensive in the U.S. and I haven't given them a try.  But my general impression is that there is not much in the way of real shortcuts.  You build up and protect your foundation of physical health, and this provides the brain the resources that enable greater critical thinking, including working memory.<p>I guess I should add in a specific reference to stress.  Acute, limited duration stress can increase my focus in a certain domain.  Chronic stress and particularly negative acute stress short circuit my working memory more than anything else.