Um, not totally sure if this i the correct place, but anyway...

When playing riffs, or going up and down a scale, is it a bad idea to get into the habit of resting my wrist on the guitar above the strings, which seems to be the natural thing to do as ive been doing it automatically. However, i think i read somewhere that you should avoid this, instead hovering the wrist and balancing the hand with your free fingers.

dont know if that will make sense to anyone
^ yes it makes sense, i wouldn't recommend resting your hand any where as you will get used to it and when you want to start doing things that require lots of movement of your hand it will feel awkward and take longer to get used to than had you not done this.