You can smooth the upshifting by double clutching.
When you shift out of first, shift to neutral and let out the clutch with your foot off the gas, then push in the clutch and shift to second and accelerate. Repeat this for the second to third shift.
Practice will help you to learn the correct engine speed and road speed at which to shift. Double clutching is better than jamming the gears, as you are trying to match gear speeds, so the gear teeth slide together smoothly.
You can downshift from 3rd to second in this manner:
Depress the clutch and shift from 3rd to neutral, let out the clutch, tap the gas pedal to slightly rev the engine, depress the clutch, shift into second, release the clutch and accelerate. This maneuver requires some practice to find the speed and engine reving at which downshifting works best for your car; it should be done only at speeds under 15 mph.
Downshifting should be a relatively rare maneuver given the low speeds at which gears are shifted. The Model A Instruction Book (owner's manual) advises that all gear shifting be done at very low speeds. The manual suggests shifting from 1st to 2nd at 5-8 mph and from 2nd to 3rd at 12-15 mph. Keep in mind that practice will help you find the optimal speeds at which to shift gears for your car.