Hi,
It depends on what you want to grow and when, for clay soil manure is a good one to add but it takes time to break the clay down and if you start with manure now your limited to what veg you can grow for 12 month really, ie spuds are out until the manure has broken down as the spuds not be a good crop until this has happend, carrots will fork in fresh manure,
I myself "depending on the size of the raised bed and if your wanting to have full salads etc quickly ie this summer and if your willing to spend ???

I'd go for removing the clay you've got and replacing it with a good compost "you could see if you can get hold of some top soil and mix compost and top soil, this way you'll have a good base to start with and from then on you can bring the raised bed soil up to a good PH. reading each year for the crops you want to grow.

But if removing the clay is impractical, then yes dig in compost/ leaf mould etc and a bit of sand/grit. not too gritty or salad veg like radishes will fork. Yes you are right good digging etc. in the late autumn dig it and leave it in clumps for the frost to help break it down. Lucky you lots of worms; they will appreciate the added humus/compost.

Thanks, its a very small bed and I was thinking things like spring onions, rocket radishes, also a couple of tomato plants left over from the greenhouse. I will work on it over time and add as you suggest in the short term