First, you should know that making contact with the ball is not as hard as people say - if you start with bunting.
The really hard part is timing... to control the bat and get your swing right, so bat and ball meet when and where you want.
Coach's note: There is more than one way to break down the swing - especially the part between launch and contact. Young hitters should be allowed to experiment to find an approach that is good for them. And don't worrying about trying to teach "rotational" or "linear" hitting - the best swings combine both.
Bring back hip around by bring back knee forward and let back foot roll up. (We used to say 'squish the bug' but now it's more 'knee in - turn on toes'... to bring your back foot up.)
Two tips that happen at the same time...
Let arms extend out, bat head sweep up and around. Finish high.
To do a one-hand release - after contact - let the bat slide off the hand underneath, open the front shoulder fully, with the lead arm still extended
To maintain two-hand contact, bring the front elbow in - like a pitcher's throwing motion - and finish with both hands to shoulder height. (Sometimes called a 'punch swing' - back arm moves forward like a boxing undercut.)
Check ball's flight only once on your second, third, or fourth step from box - depending on how hard you hit it, it should be at the fielding arc by then.
You'll know if its through, then pick up first base coach for signs.
More advance instruction by Richard Todd and other instructors is available at WebBall.com.