Chudan-Soto-Uke is effective against punches or kicks to your midsection (torso). The following key points should be remembered:

•  Speed is more desirable than power. All the power in the world wont help your block of you don't react fast enough. Try to redirect the strike rather than stop it.

• Never over-extend a block. Reaching too far with a strike will waste energy and make you vulnerable to secondary strikes.

• Move your body. Don't stand still when blocking. use angles to increase the effectiveness of the block.

• Always exhale when blocking. This increases power to the technique and helps protect you by contracting the abdominal muscles.

• Execute the block in such a way that contact is closer to the elbow than the wrist. 

Practice blocking techniques in front of a mirror. This way you can see what you are doing.  I carry this over into my dojo and when working with students, I will perform the mirror image of what I am teaching. 

Starting in Haji-Dachi stance  Right hand is in the chamber (by the rib cage, fist closed / palm up), left arm is bent, fist at shoulder height, vertical in front of the solar plexus (fist closed / palm in).  Bring the fist of the bent right arm next to the right ear (palm out, fist closed), elbow higher than the shoulder), then vertically across the chest stopping at the inside left shoulder (fist above elbow).  Simultaneously, bring the left arm to the middle of the right ribs then into the left chamber. Repeat for opposite side.   

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 Remember, without safety, there can be no Jujitsu.