I'd argue that you shouldn't.
I know it sounds counter-intuitive, but working your abs every day can actually cause weakness in your core. Hear me out.
This is for one reason: overuse. Overuse can not only cause injuries in your body, but it can reduce results from your exercise program, and the abs are no exception. If you did bicep curls every day, your elbow probably wouldn't feel very good. You would probably develop an inflammatory injury like tendonitis, which would set you back from continuing to exercise and increase strength.
When you work a muscle, whether you are exercising or doing a physically demanding activity in daily life, tiny tears happen in the muscles. These tears are good, as they signal your body to begin the inflammation process. This inflammation process swoops in to heal torn/damaged tissue, and the result is stronger muscles.
This inflammatory process can last between 2-10 days. It's important to remember that your muscles are physically weaker and more vulnerable to injury during the inflammatory process.
It's like a scrape on your arm. You'd put a bandage over the scrape to protect it until it's healed because the skin is not as tough and resistant when it's injured.
Muscles are the same way. Because they are in a healing process, they don't have their fullest capacity to contract and shorten effectively.
When this process is interrupted by working the same healing muscle before it's ready, you re-start the inflammation process. When this happens on a chronic basis, your body never has the opportunity to complete the healing process, and you can develop chronic inflammation.
The first sign of inflammation is tightness, and eventually, pain. Not only will your body feel tighter and in more pain, but you will not have gained muscle as effectively because it was never given the opportunity to heal.
It's like continuing to brush up against that healing scrape on your arm. The scape can never heal if it is constantly being stressed and re-injured.
This process can also happen with the abdominals. In my opinion, we work the abs too frequently in the fitness industry, which is probably a contributing reason why there is such widespread weakness in the "core." The scrape is always being re-injured.
Here is a 4-step process that re-considers how to train abdominals:
Many fitness trends emphasize the core, and although this comes from a good place, I believe it could be overworking the trunk muscles, leading to inflammation and weakness in the trunk.
If you're doing an exercise, like a lunge, I still recommend tightening your "core" to stabilize your spine.
However, my suggestion is to do less movements requiring our core to tighten, even if it's just isometrically, so those muscles can have space to heal and reduce the chance of overuse.
I recommend performing dedicated exercises where you are targeting the muscles of the trunk and fatiguing them. Keep these days at a minimum of two per week.
On the other workout days, work the legs and arms while stabilizing the spine whenever possible (like a wall sit or hamstring curl). When you stabilize the spine and/or place less force through the spine, you can strengthen the limbs while allowing the abdominal muscles to heal. This will result in a stronger body, better results from your routine, and less back pain.
If you want to know exactly how to do this, join Levo! I'll create a personalized plan for YOUR body leads to a more fit body with less pain.