Which drill helps train hands and improve strokes... ???

Well, one of them which I found most effective was the one arm drill.... Read the description of Drill from Steve Tarpinians - "The Essential Swimmer" book....

but I made a small variation to that drill which is a kind of preping for this drill itself....
the variation can be called handbacked-one-arm-drill (TM) :P .... in this drill what you
do is fold one arm and let it rest on your back and then swim lengths in breath... the technique is exactly similar to one you see in this video in which the non-paddling hand is resting your back
instead of you trying to hold it stiff on your side which I found quiet less comfortable...

With this handbacked-one-arm-drill you can focus on movement of one arm at a time
and experience the entry, catch and push phases of freestyle... once you are done drilling both hands you will be ready to the official.... "One ARM DRILL"... see how easy it gets to do this
drill and how smooth your body rotations happen on performing that entry and how smooth that recovery happens....

One arm drill Video :


On recovery finger-tips should drag the surface of water .... this is the KEY to make sure the next phases of the stroke go right namely the rotation and extention...

Read the "FINGER TIP DRAG DRILL" from Tarpinian's book for more info....