Sit-ups are carried out in a lying position, so you should choose a flat and smooth possible surface, which is horizontal.
If it's too hard for you, you can rest your feet on the ground to make it substantially easier.
The crunch, is one of the most popular abdominal muscle exercises and is very effective for strengthening your straight abdominal muscles.
Don't allow your lower back to arch off the floor. This is called lordosis, and it can add strain to your lumbar vertebrae.
For beginners relieve neck tension by resting your forehead on a block set between your forearms.
This exercise is perfect for starting your training.