Over the last few days I've made a concious effort to release any necessary tension in my right hand. Just a few days of this and I've seen a dramatic increase in fluidity. Especially with fingerstyle and strumming. It feels like I finally have some groove!! This has been a tremendous personal breakthrough.

Now I want to concentrate on my left hand but it's a lot harder. I know I want to apply the least pressure possible. I know I want my fingers to dance around the fretboard, rather than the more rigid and rushed movement I have now.

Has anyone got any advice on this? Possible exercises? Should I stop throwing my thumb over the top of the neck for open chords? Or is it just a case of consciously trying to play with the least amount of pressure possible? Like I did with my right hand, but it may take a lot longer due to all the different shapes and patterns.
your on the right track...being conscious of the tension..there is little reason to keep your left hand fingers pressed down on the strings..if your guitar is set up correctly-little pressure is needed to let the notes ring true..on any fret/position..tip: isolate your left hand technique..try to be in an environment that is void of distractions (outside noise..) close your eyes..or play in the dark..finger a chord..note how much pressure you apply..now take a deep breath..relax your hand (note the tension in your shoulders/neck/eyes--relax these parts also) now find the amount of pressure required to let the chord ring true..change chords and again see how much pressure/tension you are using vs need..

in watching some pros play chords.solos..they are relaxed-thus their ability to play a series of complex chords (fast solos) .. its not just knowing the fingering of the chord..its also knowing the amount of pressure to apply..

hope this helps
play well

there's that whole thing of pressing down on the note and slowly lifting off until the note is dead and repeating this over and over again. kinda trains your fingers to keep a certain maximum height above the fretboard. almost like you have a wire over your fretting hand and your fingers can't go any higher then that. works for me. economy of motion. give it a try.

loosening up your hand and good thumb posture is important too. you don't have to be rigid in it though go with what works sensibly.
Thanks guys. I play acoustic so a little more pressure is required than electric, but you are right, still not much is required at all. Just enough that the string touches the fret and doesn't bounce off when playing the string (fret buzz).

I've been making a concious effort to play with minimal pressure and it's slowly starting to sink into my subconscious. Years of too much pressure it obviously going to take time to retrain. It's amazing how little pressure you need. Even for the dreaded barre chords, such as F. I can play F with similar pressure to an open chord.

I'm certain with continued practice this releasing of tension in both hands is going to make a marked improvement on my playing ability. In fact, it already has in just a few days. Highly recommend any other beginner that isn't yet feeling the groove when playing their instrument, try giving this a go.
Your guitars position can have quite an effect on the left hand in conjunction with the angle of the wrist. If the head stock is too far away or worst still too low, you cant get the important flex of the wrist. Many classical guitarists you will note have the neck of the guitar in line with their body as opposed to the body of the guitar and virtually have their chin on the fretboard. Find a good position that suits you.