There isn't really one particular way of doing limp style succesfully. When you relax all, the most striking difference is that your tori doesn't stay balanced by itself. Shortly after that, you'll notice that your tori reacts differently to whichever movement you're doing. Both contribute to making limp style overall harder than held style. For example, if you hold all, you can just raise your arms and conk Uke on top of his head with little trouble. However, if you relax all, you'll slump to the ground before you can bring your arms back down, PLUS you're likely to be a bit off target because the chest and lumbar is relaxed. All of this contributes to a much weaker impact. However, if you test this out yourself, you'll notice that your legs will be in a good position for a follow-up attack, which doesn't happen with held style. Go on, try raising your shoulders and contracting your pecs, waiting 20 frames and then lower your shoulders again with both styles.
So anyways, if you're having problems doing limp style, you just need to practice more. You need a pretty good understanding of the game's physics and tori-anatomy (meaning which joints do what) if you are to use limp style correctly, even if it's a subconscious understanding.