The wisdom of the old masters: The old masters of Japan who laid the foundations of our sport always said that the first skill one needed to learn was ukemi - the skill of falling safely to prevent self injury during training. In modern jiu jitsu most of the action is on the floor so ukemi tends to be undervalued. Still, the same idea holds true. The first concern you must always address is avoiding needless self injury.
So learning to tap early to submissions, learning to relax your body to give way to force rather than confront it head on every time, learning the correct body postures to keep yourself safe under heavy physical pressure, these are all truly essential skills. Remember always that the number one reason for extended time off the mat and detailed training programs is injury - so learning the essential skills of lowering risk of self injury is a big part of continued progress over time. Just as every doctor begins his career with the adage “first, so no harm,” so too the jiu jitsu player must begin his career with the adage “first, avoid self harm” and learn the simple but vital skills of physical self preservation on the mat