This is the best one I’ve come across. It helps if you read the readings before Mass.
Listen as if you know that right after Mass you are going to be trapped in a situation where you will have to relate the substance of the homily to a third person, with the homilist and several other parishioners standing there. (EEEK!

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Then, add this idea I got from a talk by Matthew Kelly that I caught on the radio: when you get home after Mass, get out a notebook that you reserve for the purpose, write down what the homilist said, and add on a reflection of your own, even if it is that you don’t agree and why. Then write down one thing you’re going to do or pay attention for the next week as a result. Just a sentence.
A few months from now, when you look back on what you’ve heard and reflected on, it is awesome. You’ll start relating this week’s readings to last week’s, and last month’s, because the cycle of the readings was chosen to relate week-to-week. Your adherence to what you intended to do may or may not be too inspiring, but even that is a good thing.
The only problem is that one can get so into the homily that one’s mind can wander during the Euchastic Prayer!

In that case, it helps to study the structure of the Eucharistic Prayer and the Mass, as the meaning of things will leap out when you’ve just been reading about them.
Here are some tricks that relate to looking over the readings before Mass: Start by reading the response in the responsorial psalm. That will give you a great hint about a main message of the readings is. Then read the Gospel. Then read the 1st reading, as compare it to the Gospel with the “theme” in mind. Then add the 2nd reading (which may or may not have such an obvious connection with the other two readings.) Then go back and read the Responsorial Psalm.
Preparation, preparation, preparation and devotion, devotion, devotion. Those work the best, I think.
As for the general problem of attention, look into the literature for people with attention deficit disorder. You might also read the book, “Crazy Busy” by Edward Hallowell. He is an expert on ADD/ADHD who contends that modern society is so full of distractions and “multitasking” that it gives
everybody the trials that people with full-blown ADD have to deal with!