First choose what element it will be,
Next decide what it does ( I mean It has to do something).
Okay, now give it a cool name.
Then choose the appropriate hand signs.
Finally choose its weakness.
Here is one I made up.
Element: plain chakra.
What it does: It makes your chakra and stamina well up inside of you.
Name: final resort jutsu.
Description: A Ninjutsu that requires one of your arms to go limp for 1 day.
All hand signs are adapted to 1 hand use.
Weakness: Using up all of your new chakra.
Thanks for reading,