Okay so i've read good management can affect whether or not a dog goes on to develop symptoms of hip dysplasia so what must be avoided/encouraged to ensure the best possible health of the hips?

Things i have found when researching online:

-Not having a puppy grow too fast or become overweight.
-Not walking a puppy for more than 5mins per month of age - some say per day, some say TWICE per day, is there any consensus?  Also does what SORT of walking make any difference?  If i take my 4 month old puppy out and walk him briskly where i want to go for twenty minutes is that better than taking him out and letting him potter at his own speed round his favourite field for 30?
-Not letting puppy go up or down stairs - i have read to carry them "until 12 weeks" and not to let them rush stairs even after that until they are much older - but is the 12 week figure useful?
-Not letting puppy skid about on laminate/polished floors at speed or jump on and off furniture - until what age?
-Not taking the puppy jogging under 12 months old.
-Not expecting the puppy to jump into the car - until what age?
-Not neutering or spaying the puppy until it has reached full adult maturity - 12 months for small breeds, 18-24 for large and possibly even longer for giants?

What else can be done or prevented to keep hips healthy?

Quality, appropriate nutrition.

For a large breed I work on 5mins per month that they are and that's lead walking at a normal pace. Running around in the garden where they can choose their pace is additional and I don't count that. If you use a field I would consider the distances he's running, if you aren't moving, if you are walking he will keep following so back to the 5 min rule.
Quite frankly I don't let my dogs go up and down the stairs. I have a babygate so they cant. My youngest is 11 months and shed been up a handful of times to see it and note its boring upstairs, she was guided by her collar back downstairs, no need for them to be up there.
As for slippery flooring, I wouldn't allow at any age skidding, a grown adult can cause damage to themselves and cruciate ligament damage is common in some breeds. Either put lots of non slip mats down or change the flooring.
Its no so much the jumping into the vehicle, it's the jumping out which causes the damage, sp lift out until at least 9 months if a medium breed and if you e got a larger heavier breed at least 12 months. Even now one of my adults wont jump in at 5, have to lift her in still.
Large breeds I wouldn't be considering jogging with until at least 18 months and then would be 5-10mins here and there if you're going for a serious jog. They need to build up slowly to any real distance.

Make sure you buy a puppy from parents who have low hip scores and the generation behind them too and mykc is a great place to check out siblings and offspring of all dogs, so do your research. Poor quality food can have a bearing as well.

I found that a ramp for getting in and out of the car proved a good investment.  Useful for both puppyhood and old age.

There's no doubt that environment/sensible rearing plays a huge part in whether or not a dog will make it to a year still sound.   I remember selling one of our puppies to a couple who had had the breed before and cringing when they told me he was doing 'woosh down the small flight of uncarpeted stairs'.   Ye Gods.

And we certainly make good use of ramps with puppies of my main breed.   Plus it's more important re jumping OFF/down than up.   And again, only ambling around exercise, nothing organised or on hard pavements, for the first 6 months.   After that gradually building up the type and amount of exercise to around 12 months.  Also I didn't do 'high protein' food because to me, it can force too much growth, too fast.   Most good breeders will give all this kind of advice to novice owners of a breed where this matters.

Echo high protein diets, kibble ones which increase the rapid growth. Changed my youngsters to raw, it was either that or adult kibble at around 5 months old.