What are some good methods for focusing and concentration for laborious reading and study?
Even if there is doubt of authenticity of this, St. Thomas's
De modo studendi (https://isidore.co/aquinas/DearJohn.htm) has good advice:
Quote- I command you to be slow to speak, and slow to go to the conversation room.
- Embrace purity of conscience.
- Do not give up spending time in prayer. [← Probably the most important!]
- Love spending much time in your cell, if you want to be led into the wine cellar.
- Show yourself amiable to all.
- Do not query at all what others are doing.
- Do not be very familiar with anyone, because familiarity breeds contempt, and provides matter for distracting you from study.
- Do not get involved at all in the discussions and affairs of lay people.
- Avoid conversations about all any and every matter.
- Do not fail to imitate the example of good and holy men.
- Do not consider who the person is you are listening to, but whatever good he says commit to memory.
- Whatever you are doing and hearing try to understand. Resolve doubts, and put whatever you can in the storeroom of your mind, like someone wanting to fill a container.
- Do not spend time on things beyond your grasp.