Sardines. As well as fatty acids, make sure you're getting enough vitamins and minerals in general.
You can start a working today in fact, before the Moon goes Void. It's in Virgo now, even though it is not Mercury day you can still vibrate a Mercury mantra or a rune and affirm your mind is improving in beneficial ways for you.
Learning improves the mind. Science, or a language, or music, or even a new hobby you are passionate about. Studies have shown studying music helps with all areas of learning.