Goosey
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I'm happy with one set, I do find curls very boring. If I use dumbbells any grip position you prefer.
By the time you finish a set of curls and you need to sit down I think you know you've done a good job.
If you're using DB's rotate your hand clockwise as far as it can go and DON'T lose tension throughout the set.
Lean forward slightly when at the top and as you lower lean back this guarantees constant tension.
By the end off the set you want your arms burning and legs wobbling.