Note: There are many "right" versions of this sign.
General sign for first (the most flexible).
Meanings:
"First of all"
"Original"
"Prototype"
This is a variation of the same sign. Notice how the index finger
moves past the thumb instead of stopping at the thumb like in the other
variation.
Both ways are okay. I suggest you do the first variation, but that
doesn't make this version wrong. See below for even more ways to sign
"first."
This version brings the index finger to the thumb where it makes contact
but doesn't go past.