There is a technique I see none of the other comments have hit upon. First, know concentration is a skill, so develop that. I can tell you how to muscle up but

There is a technique I see none of the other comments have hit upon. First, know concentration is a skill, so develop that. I can tell you how to muscle up but if you can't pull up then knowing how won't help. You are able to convince yourself you're interested in something by asking questions about it. Create the space in your brain that wants the knowledge to be in there. Find a question you genuinely want to know the answer to. There's usually at least something. This is how I was able to maintain focus on reading atomic physics, funnily enough, it's now the most prominent thing I remember from my degree.