• 1. Warm Up: Before a full core workout, march in place for several minutes while swinging your arms, or dance to a few songs. It's safe to skip this if you've already warmed up through other activities.
• 2. Form First: Good form means aligning your body as described in the exercise instructions and moving smoothly through an exercise.
• 3. Reps Second: Quality trumps quantity. Do only as many reps as you can manage with excellent form. Likewise, hold a position only for as long as you can manage with excellent form. Plan to work up to the full number of reps or seconds gradually. Once you can do a full set, consider adding a set (up to three sets).
• 4. Feel no Pain: Core work shouldn't hurt. Stop if you feel any pain (especially if it's lower back pain). Check your form and try again. If pain persists, check with a doctor or physical therapist before repeating that exercise.
• 5. Practice Often: You'll see the best gains if you consistently do core exercises three times a week.
• 6. Don't believe the Photos: Photos tell only part of the story. Photos can make core work look easier than it actually is. Do your research, and carefully read instructions when learning about the tips and techniques for each exercise.
• 7. Brace yourself: Tighten your core muscles before starting the "Movement" in each exercise. Here's how: while sitting, standing, or lying on your back, gently but firmly tighten your abdominal muscles, drawing your navel in toward the small of your back. Tuck in your tailbone slightly, too. Once you're braced, a gentle push from any direction should not cause you to lose your balance. Some trainers suggest imagining that you're pulling in your muscles to zip up a tight pair of jeans. Either way, practice makes perfect. Try bracing or zipping up for 10 seconds at a time while breathing normally.
• 8. Reach Beyond Abs: A rippling six-pack and a weak back are a recipe for disaster. So don't just focus on abdominal exercises that buff appearances. A program that works all core muscles protects your back and boosts sports performance.
• 9. Be Flexible: Core flexibility is as important as core strength. In fact, too much strength without flexibility can make your back throb and interfere with smooth, powerful moves in sports like tennis and golf. So don't skimp on stretches.
• 10. Start With Stability: Begin with stability then add instability. Master exercise movement patterns, such as lunges, bridges, and planks, on a flat surface. Core work gets harder when an unstable surface, such as a stability ball or Bosu, is introduced because your muscles have to work harder to hold a position steadily or stabilize you while moving. Take time to perfect hard exercises on a stable surface before shifting to an unstable one.
• 11. Drop Down: If it's too hard, drop down. Do fewer reps or hold for fewer seconds. Still too difficult? Try an easier variation of the exercise. If you're still struggling, try fewer reps (or seconds) of the easier variation.
• 12. Easy, Move Up!: If it's too easy, move up. As it feels easier to do exercises with excellent form, first add reps (up to 10) or seconds. Next, add sets or try a harder variation. As you move up to more challenging exercises, leave the simpler ones behind.

From Harvard Health Publishing: Chech out Full Article Here!