I prune mine in winter and as hard as possible

I've been chopping 'too long' branches off mine for the last 2 months, and it doesn't seem to mind, but I'm no expert.

Depends if you want the flowers. If you do then prune after flowering. The berries aren't worth waiting for as they are small and mingy. This is what I do but I keep mine at about 5 feet.
If you don't want the flowers (and they are very pretty) you can do it in autumn. They don't seem to be fussy about when you do it!

It has already finished flowering [not many as this was its first year] so if I prune it now will I not get ant flowers next year? I want the flowers.

Foxhaven, I have just scrolled down to E at the bottom of this page, then clicked on 'Elder' . . . there are various questions on this shrub from GoY members: have a look. Spritzhenry says that she cuts hers back in Spring so that she can enjoy the flowers, and she is a very knowledgeable gardener.

If its a fairly young bush it might not need pruning at all yet. Pruning is only done really to keep the plant the size and shape you want. I shall stick to pruning after flowering as it works for me. But if you decide to prune in Spring do it early before the new growth or you will cut the buds off.

My understanding is that you hard prune in spring if you want a bushy plant for the leaves, and immediately after flowering if you want flowers. I always do the latter and it has always worked.

There is no need to prune it at all unless you want to control the shape and size. If it is still a young plant I suggest you leave it and enjoy any flowers you get this year, and only trim it then if it is getting too big or out of shape.