Here are 20 abdominal exercises(abs) techniques to help strengthen and tone your core muscles:

1. Crunches: Lie on your back with knees bent, hands behind your head, and lift your shoulders off the floor, contracting your abs.
2. Reverse Crunches: Lie on your back with knees bent, lift your legs off the floor, and curl your hips towards your chest.
3. Russian Twists: Sit on the floor with knees bent and feet lifted, twist your torso from side to side, touching the floor on each side.
4. Plank: Start in a push-up position with elbows bent, forearms on the floor, and hold your body in a straight line from head to heels.
5. Side Plank: Lie on your side with legs extended and prop yourself up on your forearm, lifting your hips off the ground to create a straight line from head to feet.
6. Bicycle Crunches: Lie on your back with knees bent and hands behind your head, bring opposite elbow to opposite knee in a bicycling motion.
7. Leg Raises: Lie on your back with legs straight, lift your legs towards the ceiling, then lower them back down without touching the floor.
8. Flutter Kicks: Lie on your back with legs straight, lift legs slightly off the ground, and alternate kicking them up and down in a fluttering motion.
9. Mountain Climbers: Start in a plank position, bring one knee towards your chest, then quickly switch legs, alternating back and forth.
10. Dead Bug: Lie on your back with arms extended towards the ceiling and legs lifted in tabletop position, slowly lower opposite arm and leg towards the floor while keeping your core engaged.
11. V-Ups: Lie on your back with arms extended overhead, lift legs and torso simultaneously, reaching hands towards toes in a V-shape.
12. Standing Side Crunches: Stand with feet shoulder-width apart, raise one arm overhead and bend sideways, crunching to the side.
13. Hollow Body Hold: Lie on your back with arms extended overhead and legs straight, lift shoulders and legs off the ground, creating a “hollow” shape with your body.
14. Spiderman Plank: Start in a plank position, bring one knee towards the same elbow, then switch sides, alternating back and forth.
15. Sit-Ups: Lie on your back with knees bent, hands behind your head, and sit up, bringing your chest towards your knees.
16. Scissor Kicks: Lie on your back with legs straight, lift legs slightly off the ground, and cross one leg over the other in a scissoring motion.
17. Russian Leg Twists: Sit on the floor with knees bent and feet lifted, hold a weight or medicine ball and twist your torso from side to side, tapping the weight on the floor.
18. Toe Touches: Lie on your back with legs straight and arms extended towards the ceiling, lift your torso off the ground and reach towards your toes.
19. Plank Jacks: Start in a plank position, jump feet out wide and then back together, keeping your core engaged.
20. Side Crunches: Lie on your side with knees bent and hands behind your head, lift your shoulder towards your hip, crunching to the side.

Incorporate a variety of these abdominal exercises into your workout routine to effectively target all areas of your core muscles and achieve a stronger, more toned midsection.