As a person who is not diagnosed ADHD or autism (but has traits of both), what's made sense for me with meditation is that it's about relaxed attention. Choosing to focus your mind on something specific (for example, the sensations of breathing in and out, or even something simple like counting). Recognize that yes, your mind will wander, and you'll catch yourself drifting off to think about the show you just watched or the burrito in the fridge or how stupid meditation is... And that's normal. The practice of meditation is catching that your mind wandering, acknowledging that with kindness and without judgment, and going back to what you were focusing on for your meditation. Don't be hard on yourself! Every time you catch your mind wandering, you are actually SUCCEEDING (because you recognized it), and are PRACTICING catching your mind wander and practicing getting back on track. :)

For me, that's what made it work. Focusing on nothing or letting my mind wander just leads to anxiety about doing it wrong and boredom, but gently focusing on something neutral and just practicing catching myself wandering is something I can do.