I got my first on my first try, and all but 2 out of thousands over a whole career. ?Reason -- ?mixed hand dominance [Better to be lucky than smart!]? -- and definitely No Fear.
But I know you don't want to hear that.
I think the clumsiness lies in anxiety-driven inhibition. Third year, med school: all the invasive procedures were taught by rsidents who were themselves so anxious about doing that stuff that it was contagious, and led to repeated failures, repeated sticks, persistent guilt about inflicting needless pain. Then I hit my Neuro clerkship, and the Chief Res showed me in the calmest, most laid back manner, how to do a smooth, non-traumatic LP. It was not in the technique; it was all in the attitude.
That's how I taught my own residents.
So: find the coolest, most laid-back, most patient attending or senior res, and rotate into his/her room, let him show you, then guide you. [You'll be amazed before you are half-way through!]
No Fear.