The two proportions of the NAHRA test that most people have trouble with switching over, is the quarter sit to flush and the trail.
Upland-Quarter
The upland portion in intermediate doesn't require a sit to flush, you will be asked to quarter. Usually they like to quarter up into the marks. So you take your dog from free range quarter into, steady for a double, which can be tricky. Quarter can hype many dogs up, so practice this. Now when they say quarter they don't mean the dog has to run any particular pattern, they just have to go out and illustrate they know how to effectively hunt an area. Also you control how fast or how slow the hunt proceeds, keep him in gun range and be sure to keep reasonable control to be able to bring him back to steady. You'll know why when you reach the top of the hill and the double just goes off

. Sometimes a dog reaching a certain point top of the hill etc. is what sets the marks off, you'll have an area to get them back into heel, be sure you know where that area is, because if the dog reaches the set off point without you, getting control. STUFF HAPPENS!!!!
The Dreaded Trail
Intermediate trail can include a turn and can be pretty involved. The degree of difficultly can range from very straight forward, to extremely challenging. Trail is the aspect most people go out on, because they don't train for it. So much so that a lot of people get upset if they put the trail at the beginning of a test rather than it being the final series

. This aspect the dog has to do entirely on his own, and he has to run a significant distance away from you and find the bird with no help. If he gets lost he needs to know how to return to a scent pocket, work it out, and continue on until he finds the bird. They also have to show that they are indeed trailing not just running all over. All you get to do is stand there and wait, which is very nerve racking, even with a master trailing dog

. It's a good idea to go out (especially with a fast dog) and teach the dog how to stay on the trail, how to find and go back to scent pockets, etc. When You put out a trail mark it in away so you know where the scent pockets are, and pay attention to wind direction, get a pretty good idea where the scent will travel, it makes it a lot easier to know when the dog is actually trailing, vs. running all over with no real direction. This type of training more than anything else teaches you how to read your dog, and you'll begin to know when he has scent, and when he's messing around. This makes it a little easier to stand there and watch. That is until the judges tell you, re-heal your dog and you have one more chance, or my favorite let's see if the next dog can do it.
Couple of other things
Air you dog well and Train him not to lift his leg all over the trail, judges really dislike that. It messes up the trail. I've seen one hard core miscreant dropped for it.
Train your dog to handle off the trail, once he has the bird... It's much more impressive to sit your dog and cast him over to meet you than running down to the end to ensure he's not going to get back on and contaminate the trail.