[paulz_]

It sounds like you're trying to improve you're ability to focus as much as anything. Consider mindfulness meditation.

Essentially you sit in a quiet room and focus on your breath. You'll find this very difficult and your mind will wander. When you notice that your mind has wandered return your attention to the breath. Do your best not to be frustrated by this experience. You'll find even after much practice your mind still wanders away from the breath constantly. This is normal and happens to everyone.

Don't beat yourself up for your thoughts drifting while practicing. You almost want to be smiling at noticing how much the human mind does that. Think more on those terms.

You may find as you practice you'll get better at noticing your mind wandering in every day life and returning your focus to what you were doing. I also find that when practicing daily focus in general comes more easily.

[kar5pt]

I've been doing mindfulness meditation for around 7 years now (I also have ADD). It helps my focus a bit, but comes with diminished returns over time. I meditate for other reasons but I wouldn't recommend it just for focus. The amount of time and effort it takes isn't worth the marginal benefit to concentration. I still struggle with the same focus problem OP does.

[Pyramus]

YMMV and there will be definitely be people like yourself, but from my own experience and the research I've read, this is exactly what mindfulness meditation is targeted at:

1. The ability to detect the mind wandering off.

2. The ability to re-direct attention.

There are studies showing that neural circuits linked to 1 + 2 are strengthened when doing mindfulness meditation. This benefit is specific to mindfulness meditation, and hasn't been shown for other types of (secular) meditation like transcendental meditation or relaxation exercises.