Here are a few to get you started. Remember, start out slow!
Squat at Horse Width
1. Stand up straight with your feet at a width that is your leg position in the saddle. Fold your arms across your chest, elbows close to the sides of your body.
2. In one smooth motion lower yourself towards the floor in a squat, as if to grasp and object at your feet. Allow your upper body to bend naturally as you lower yourself. Keep your weight centered over your insteps NOT your hells or the balls of your feet.
3. Align your knees with the inside of your feet, without pressing them to the outside. Lower yourself slowly and as far as comfort allows but not too far!
4. With your legs push hard into the ground and return to standing position.
5. Repeat 7-10 times OR as comfortably as you can
Need a step or stool 4-12 inches high
1. Place the step directly in front of you. Place one foot on the middle of the step.
2. Shift your weight forward so you can feel it align with your instep. Allow your upper body to lean slightly forward.
3. Forcefully push down into the step with the supporting leg and move your body up and over the step.
4. Come to a standing position with both feet on the step.
5. Leaving the supporting foot on the step, lower your body in a controlled manner back to the starting position.
6. Repeat 7-10 times each leg, comfortably!
If you have access to a gym, leg extensions and leg curls will help. If you don't, stairs are a good alternative for leg exercising. Walk the stairs though, don't run. You have more control and can concentrate on flexing your thigh and calf muscles.
I recommend getting the book, it's amazing and each exercise shows you how it helps with your riding.