Lets assume mostly HPR instincts and strong hunting ...
Only hunt on a long line until you've got consistent stop on the big temptation of game flush. Huge pain in the proverbial, but the more flush / chase action she has the harder it will be to pull back. Dont believe the "let them chase birds, they will grow out of it and learn they cant catch them" line. That might work if you have an endless bag of pigeons to throw i.e. you have control of repetition and you have the birds, but I very much doubt it will work at 100 yrds when at speed and "on it". If you are working in UK you just don't have the space, land, roads, safety comes in. At this stage every single chase is a reinforcement of how much fun that is.
You have to proof the stop to chase with increasing distraction/excitement. If you can build (or have) a strong ball drive/ dummy drive in a game free environment you can (again starting on a long line) blow stop on the outrun / chase. You then have complete control, if the dog ignores you it gets pulled up short. Initial stops before the dog gets up to full speed, you're trying to reinforce compliance and give an opportunity to learn. If the dog knows well what a stop is, it must believe its not optional depending on situation as it sees it.
Tempt with everything, thrown ball dummy when walking to heel (and on long line / lead). Maybe try bolting rabbit on a spring a few times, don't think it tempts fools many dogs, so probably not worth repeating much.
Then to real game which is the real temptation. Anything in which you can control the chase and get the dog to comply with the stop under temptation of scent and movement of game, rabbit pen work, engineered point / flush using bird launchers, working on a ling line through a squirrely wood. As you are asking the question, you will very probably have to see a trainer with access to birds and launchers and rabbit pen, because most people don't have those facilities themselves.
I would say having got to this point nothing else really matters until you have control of the chase, so you will be restricting all off lead action to game free or very controlled game situations for probably 6 or so months. The alternative is the dog cant be used as a gundog, you might have great obedience in a game free environment, you might have all the lefts rights, backs on dummies, blinds, water and all the bells and whistles, but as they say, you've either got full control under the ultimate temptation ... or not. Cant use it for beating if it chases, cant use it for picking up and send it into woods for a seen retrieve in case it bumps a live one and takes off and clears the next drive....
I sound like a misery, not trying to be... its a phase that any dog with even half a hunt in it will go through, so on the plus side it goes with some drive, but for me it is "the" difficult one. And you may guess that I messed this up with my first GSP, and so far not messed it up with my second
Other more experienced opinions will no doubt be along shortly
