Wandering Star
The Living Force
First thing to do is to understand the machine. Only then can you try to take it apart, clean the parts, and put it back together.
Books like "Thinking Fast and Slow", "Strangers to Ourselves", "Blink", "Inside the Criminal Mind" (Samenow is VERY good), etc.
Of course, in "The Wave" series, I spend several chapters talking about how we are programmed, how it works on the chemical level, and what efforts are required to overcome this programming. I've been told by a number of people that just reading "The Wave" series has helped them get a grip on their thinking.
I'm sure some other members can follow my line of thinking here and add other suggestions in that trajectory.
It also helps to be in good physical condition. If you have inflammation in the brain, you can work until you collapse and won't make much progress. So, diet is one factor. There are other health factors and this would be where EE might come in. Many of us have been experiencing enhanced thinking by using HBOT (Hyperbaric Oxygen Therapy) chambers. That really only might be necessary if there are health issues to deal with, though certainly added oxygenation to the brain can't help but be a good thing.
In short, optimizing from every angle is the best approach.
There is not much to add to the wisdom provided in these two comments and that of the rest of the people who have commented.You received very good recommendations, but I think it's important to highlight the perspective of developing being if you're to focus. I have found that rereading the Wave, especially after crucial experiences, helps to re-focus big time. Your aim gets sharper and clearer, as you understand better.
My meditation and focus always improves on reading writings that speak about the truth and based on the truth.
And as Gaby says, with each new reading of the same text, you learn more and see things that you hadn't seen before, with moments of inspiration like "aha, so this has happened to me because of...!" .
In fact, you suddenly realize that you have been meditating for a while without really reading the text and many understandings are reached.
Very good advice.