I would also work on directional commands and you can then send them out to blind retrieves and then you can progress to double blinds etc. If they don't already quarter/hunt properly I'd do that too and you can then have them hunting for stuff you've planted along the way. Start to combine hunting and retrieving as they should blend in together.
You could also work on their stop to shot and you can combine that with a retrieve. I have a starting pistol but more often than not I use party poppers, they're cheap to buy and make a surprisingly loud crack when you set them off. Obviously you have to take all the stuff out of them first as you don't want it littered all over the place but they still work perfectly well. Get the dog hunting in front of you and have a party popper and a dummy in your hands, at the appropriate moment pop the popper and - this is the important bit - at the exact same moment throw the dummy as far out as you can. The dog should instantly stop and mark where the dummy has landed and you can either then direct them to the retrieve or hunt them on a bit more and then send them back etc. etc. It takes a bit of practice to pop the popper and throw the dummy at the same time but once you've got it it's easy enough to do it in one sort of sweeping motion.
This is also a good exercise to do if you can get a helper in, you hunt the dog and they stand out somewhere in front and pop the popper and throw the dummy - if you're always training your dog by yourself they can become used to the idea that all retrieves come from you when in reality on a shoot or in a trial it never comes from you, they retrieve what the guns shoot, and in a field test they retrieve the dummies launched by the judges so it's important for them to get used to marking something thrown/shot by someone else that you send them out to. Start off by having them throw it so it's relatively easy for the dog to find, let them be able to see it the first few times and then you can up the complexity by having them throw it into heavier cover so the dog has to actively search for it.
Hunt the dog up towards a small obstacle (fence, wall, ditch etc.) then have your glamourous assistant 'fire the shot' and throw the dummy out past the obstacle and then send the dog out so not only do they have to go out for the retrieve and negotiate the obstacle but they also have to find the dummy as they won't have seen exactly where it landed.
Hunt the dog out in front of you, pop the popper and throw the dummy out into cover but then whistle them to turn and hunt them back the way they came before stopping them and sending them back for the retrieve. This really tests a) their control and obedience and b) their memory.
Sit the dog down and throw a dummy out behind them over their head and one out to either side. Send them out in a random pattern to retrieve each dummy but sometimes stop whistle them when they're halfway there and redirect them back to one of the other dummies. Sometimes pick one of the dummies yourself while they wait. This is a great control and direction exercise. Put the dummies out in a similar pattern without the dog seeing and then direct them out to get them one at a time, they have to learn to trust your directions even if they haven't seen what's there.
When the dog is returning to you with a retrieve throw another dummy out over their head or to the side as a distraction, they should continue back to you with the retrieve they've got.
On the delivery to hand if he was doing this consistently before it's just a matter of not accepting anything else. I never pick up anything my dogs drop on the ground, they have to put it in my hand. I say 'nah' (which they know) and shift back slightly and hold my hand out again so they pick up whatever it is and put it in my hand.
