OP, your best bet for meditations would probably be visualization ones, if your goal is focus. The idea is to generate an image or concept in your mind and focus exclusively on that, to the preclusion of all other influences and distractions. In Buddism they call it single-pointed meditation. In their tradition they focus on a concept, a suttra, a bodhisattva, etc... but you don't have to do that. It does help though if the point of focus is something positive or promotes higher values, because you'll be focusing on that for lengthy periods of time and it will influence your general consciousness.
However, usually people can't focus because they are ungrounded, and they're not grounded because they overuse their minds, have improper diet, exercise, or too many distractions. I don't think that concentration meditations are the solution for such people but rather emptiness meditations which stop the mind completely. These are more restful. Sometimes focus is hard because there's underlying exhaustion and an inability to let go. It's only by being able to witness mind that you realize what is extraneous and then take steps to stop it.