I find guided meditation and mindfulness exercises to be incredibly helpful in assisting in learning 'how' to sit, focused for a period of time. There are some good free relaxation apps that use guided meditation to keep the listener focused, and to help them refocus when the mind wanders. I imagine it would be especially helpful to people who find it hard to 'let go', who find themselves distracted by physical sensations or external stimuli to a point where meditative practice is not possible. Many guided meditation techniques work with these distractions and incorporate the refocus of the mind into the practice. I'm not saying it's for everyone, but if you're interested in finding out if it works for you, and distractions are impeding your attempt, one of the guided apps might help.