I have been trying to achieve the big O, hands free for about three months now. I started with a Nexus G-play and a Naughty Boy (sit and rock type) and while they provided great stimulation and pleasure they just would not get me there all the way. Also I bought a Aneros Helix with similar results.
Then came the G-spot dildo. After getting a new toy my wife handed me her Temptress G-spot vibe. Small but with the angled tip (and a firm hold) I tried it out. With some small thrusting and turning I could get worked up twice as fast and have more control over the pressure. The wife has use my new Deep Secret probe on me and that is a great help. Like ScottA was saying, it help's the guy to concentrate on the stimulation he is receiving.
From my looking around here and the internet, almost every one says it will take time and practice. Some say up to a year! Seems to me that when you are experiencing something new it will take some time to find what works best. When my wife had her first O it took about a week for her to learn 'what, where and how'. For most guy's I would think it would take longer. Just means more fun!
So enjoy the journey (I am) and keep 'practicing'.