The secret of becoming really bendy and really good at handstands...

There is no secret.  If you are dedicated, work hard, use good technique, don't over rush it, then you will improve.

There are also no quick fixes, it takes time.  For steady progress without plateauing or getting injured you will also need to work with correct technique, for example learning a bad shaped handstand, or just lifting your arm from the floor, is not going to progress you to a one arm handstand, you are better off stepping backwards and getting the shape right/doing the correct progressions and then the one arm handstand following these correct progressions will happen a lot lot quicker and consistently.

I currently teach acrobatics to two awesome identical twins.  When I first met them it was amazing because they were both identical in flexibility, their bridges were identical in shape and bend, their splits also looked very much the same (they both had and still have very good flexibility).  As they have got older then their flexibility is no longer the same as each others.  We only train twice a week.  One broke her ankle (skiing) and missed a chunk of lessons.  But she has done enough to maintain what she already has, the other has been working hard and consistently and her back flexibility is becoming really rather amazing. It is fascinating to watch. 

Me by Jason Lunn, these hands work hard to keep me upsidedown :-)