Control your breathing. We have to be able to keep the core stable and breath at the same time. Someone might be able to get away with holding their breath for a short effort like a max lift but anything that requires any length of time, is going to require proper breathing technique. Practice diaphragmatic breathing "belly breathing". As you inhale, the stomach rises/expands. As you exhale, the stomach draws inward. This is the first step to core control.
Organize the spine. We don't want a flat spine. The goal is neutral. If you find yourself arching your back or your trunk collapsing forward, you should probably stop, unload some weight and retry the movement with proper form. Even if you can still get the job done, it’s not worth the damage you're doing to the joints. In the long run you will have more potential with proper form.
Resist the ground. By this, I mean create torque through your feet, knees and hips. Whenever you go to lift something, drive your feet into the floor by attempting to drill them into the ground, pressing your knees outward, and squeezing your butt.
Engage the abdominal muscles. Fight for that neutral spine! This is last for a reason. There is a lot that needs to happen before you "tighten your stomach". There's no point and it is extremely difficult to brace yourself in a poor position with improper breathing. You may need to start off by practicing this lying down. Lie on your back with your knees bent and feet flat on the floor. Practice flattening your back into the floor and holding that position. Next add heel slides, leg lifts, arm motions or really any movement. You should be able to hold that neutral spine position despite what your legs and arms are doing. Once you have mastered it on the floor progress to standing activities and then dynamic or athletic activities.
