It really isn't a case of how, it is more a case of how long.

Put it out of the way somewhere safe (if you have neighbours like me, they may nick it). If it is open to the elements it really doesn't matter too much but there is debate on that. Putting something like sacking over it is a useful way of making sure it doesn't dry out. Leave it for as long as you can. 1 year is really minimum, even though some people try using it after about 6 months, and up to 3 years or even more is fine. Most folk think a couple of years is about as good as it gets. You can test when it is at its best because it goes all crumbly and doesn't smell, no let's use the Samuel Johnson word - stink, any more. When testing it a good pair of gardening gloves is a good investment and, strangely enough, it should smell almost sweet in an earthy sort of way. Never mind being afraid of the unsavoury aspect of it, it really is the greatest thing if you are a serious gardener. :o)) If you need to use it early then make manure tea out of it by dropping some in a bucket of water and using the liquid in just a few weeks.

It needs to be well rotted as it can damage.....even kill plants if it is used fresh

As well as keeping it for a few years you could bulk it up by mixing in some straw. The straw will rot down at a similar rate to the manure.

Thank you all very much for taking the trouble to reply - your comments have been very helpful.