Grids are great for teaching horses because it sets them up for success. There's no guessing on takeoff spots, no single fences to get nervous about, allows for a quiet rider who just sits up there and stays out of the horse's way. If I were you, I would do:
1) Set up four poles spaced 4.5' apart (trot stride) Trot through it keeping your horse rhythmic and straight. Once he's good with that, place a small cross rail 9' after the poles. Trot the poles and stay in 1/2 seat over the cross rail. Best if you can set this up in the middle of the ring so you can turn alternate directions after the cross rail each time. Ideally your horse will canter out of the cross rail. Be sure to come back to trot before repeating the exercise.
2. Set up two cross rails spaced 18' apart. This is a one stride canter distance. Horse can either trot in or canter into the first jump, then canter one stride to the second. Your job is to keep the horse traveling forward and straight. If he keeps stopping or ducking out, you do not have enough forward. You can build up the fences to verticals once you are ready. Again, set it up in the middle and change directions after the second one each time.
3. Two ground poles, or cross rails spaced 4 strides apart. (48') Trot over center of first one and make large circle that takes you back over the same jump. Then proceed straight to the second fence, again make a big circle and come back over same fence. Center, change direction, blah blah blah.
4. Bounces. Soooo much fun. Place two poles or low verticals 9' apart. Canter them. Stay in a light seat with some contact on the saddle. You want to be able to regulate your horse's canter so he doesn't barrel in full speed. This exercise teaches the horse to use impulsion rather than speed to get the job done. Once you can do 2 in row, add a 3rd, then a 4th. Stay out of your horse's face. Grab mane if you have to.
5. Once you get the idea of what each thing does, go nuts. Keep everything in 9' increments and have fun with it. My favorite for horses who jump flat is a 2 pole bounce > 18' to a low oxer. If you find your horse is cheating and putting in more or less strides than he should be, use a ground pole every 9' between fences to regulate the stride.
Remember, as the rider and the person who is teaching the horse to jump, your job is to not overface him or do anything to sour him to jumping. Stay out of his face. Use a neck strap or grab mane, but make sure you give a good release so he can learn to use his neck. Do not jump ahead. You should be in a light to full seat on approach to each grid. Let the first element push you up into 1/2 seat and then just hold your position through the grid. If you find your horse getting frustrated, take things back a notch and simplify whatever grid you are jumping. Do not over drill. If you horse gets it, loves it, and did exactly what you wanted, go out for a relaxing hack or change to some other exercise.
As you can see, I love grids. Have fun.
You just have to see your distance...you don't have to like it.