Just been doing a load - and this tip might help starters.
Always do the scribed joint first.
Mark the centre of the round bit on the back, so the whole circle is on the scrap part of the wood. Get this bit right. I found a washer of the same diameter with a small hole which made a good centre finder. Note the distance for later use - lock off say a set of calipers or marking gauge.
Drill a 1 1/4" hole with a good holesaw preferably using a pillar drill. Once halfway through or so turn over and do from the sculpted side.
With a square cut piece of scrap line up on the back using a set square and hold firmly. Remove the set square. Mark round the profile with a sharp pencil.
Mark the waste. ;-)
With the set square, continue the line of the sticky out bits down into the waste and cut with a decent tenon saw - doesn't matter how far down you go.
I then use my compound mitre sliding saw to do the main cut - obviously stopping in the waste. Finish that cut with whatever fine hand saw suits - most tenon saws won't be deep enough.
Then remove as much of the waste as possible, and do the final near horizontal cut for that little tang as carefully as possible. Finish with a file.
Any other tips gratefully received. But I'm getting pretty well perfect ones this way.
So my favourite old chippy, George, words ain't needed:-
'If your mitres do not fit. fill them full of putty and s**t.'