I think it depends on the type of hydrangea that you have. A light prune in spring is ok, but remember that flowers are produced on new stems, so if you do prune you may not get as many flowers.
As for the best place to plant them: they like a moist soil (but with good drainage) with some shade.

With most Hydrangeas, the flower buds form in lat summer and fall, and bloom the following spring, so the best time to prune is immediately after the spring bloom.
If the bush is severely overgrown and neglected, it can get a severe prune in early spring to rejuvenate it, but then it won't bloom until the following year. Here in the desert,we grow them on the north side of structures and trees, so they have bright shade. In the UK, they can probably take a little more sun. If it has blue flowers when you buy it, any signifigant chalk in the soil will turn the flowers pink.

It does depend on the variety of Hydrangea. The one you see planted most everywhere in the UK is Hydrangea macrophylla, either with those big, round mophead flowers, or the more delicate lacecap ones. The mophead flower types are the ones affected by soil ph - chalky soil means pink flowers, acidic soil gives blue flowers, neutral ph often gives a sort of lilacy pink shade. They generally can't be pruned without loss of flowers, so usually, in April, its just a case of snipping off any dead stems and flowerheads. Renovation pruning is possible on old specimens, usually involving cutting out some of the major stems at ground level and leaving other stems alone so that at least some flowers will be produced.

Hydrangea paniculata varieties have cone shaped flowers - these can be pruned down low in autumn and they will still flower the following year and flower colour is not affected by soil ph.

None of these likes soil that dries out completely in summer, so people usually plant them in shadier areas (but with some sun exposure) to avoid that problem.

The literal translation of 'Hydrangea' is water vessel. That should be a clue of what it likes most. This bush loves its water so as mentioned above; damp moist soil. Partial sun to bright shade is best with rich dark compost. Pruning depends on variety.

lol Bathgate! You have just reminded me of a holiday we had when the children were small. We drove all the way to Brittany from Scotland and when we arrived at our destination I remarked to OH....'There are Hydrangeas Everywhere here' they must get a lot of rain. Well, rain it did...for ten days. It poured. Miserable! Scott has never forgotten my words. :)

Agree leave the flower heads on over winter to protect the new buds from any frost (Tugbrethil probably doesn't
have that problem often in Arizona!). Then cut them back several inches to just above a bud. As long as there are some buds left on the stem you should be OK.

oh Karen, sorry about your holiday. What a brutal lesson on Hydrageas. Reminds me of whenever I need a rainy day, I simply plan a softball game at the local park. That's a guaranteed all-day soaker.

Lol Bathgate!

Stera's right. We don't have much trouble with frost on Hydrangeas--Bougainvilleas and Hibiscus are another matter!
Karen and Bathgate, here in the arid Southwest we have tried all sorts to try to make it rain. No matter how often we use the hosepipe, nothing helps perk up the plants like a good soaking rain! The only thing that seems to work consistently is washing the car. That only results in what we call an "Arizona mudstorm", though: a roaring dust storm, followed by just enough rain to make it stick! :D

Yuck! That sounds pretty gross! ;)