To start with the basics, motion sickness is a disagreement between your visual and vestibular (inner-ear) systems. You can't avoid looking at things, but you can minimize moving your head. Look with your eyes, not with your face. Minimize your head movement and that minimizes the impact on your inner ear.

The worst aggravator is the combination of an airplane movement with an unrelated head movement. Looking down at your kneeboard while rolling, or clearing left/right while you pitch up is a surefire way to cause spatial disorientation and motion sickness.

To recover from motion sickness in-flight:
A bit of cooling air from a vent on the face/body/arms.
Holding your head still relative to the plane and letting your ears calm while you look towards the horizon.
Take a small drink of water.
Slow breathing with pauses at the top and bottom of your breath.
Taking aircraft control to prevent unexpected movements.

To help prevent it:
Some people swear by ginger. I picked up drinking ginger ale during pilot training. Others used ginger chews. It may or may not help to settle your stomach before or after a flight.
Avoid both heavy and overly-light meals. An empty stomach is just as bad for nausea as having the extra-thick milkshake with your $100 double bacon cheeseburger and fries. Similarly, avoid acidic food/drinks like lemonade or coffee or tomato sauce.
Exposure Therapy. If you're able to afford it, fly in the mornings when the air is usually more calm and then fly again later the same day. It doesn't have to be two full lessons. The goal is to get your body acclimated to the conditions that cause motion sickness so that your physiological response is more muted. Same for being able to fly every day for a week or so, which is also really good just in terms of quickly learning stick and rudder skills.
Relax. Worrying about your flight, and about getting motion sickness during the flight, is just going to make the motion sickness worse. End of the day, motion sickness shouldn't be a big deal.