How would you balance: N2 + H2 --> NH3?
Balance the nitrogens first!
Is the equation above balanced? Do not take my word for it. I might be wrong, or I might be trying to trick you.
To put this another way, when you receive change from a banknote after you make a purchase in a shop, would you know whether you had been short-changed?
I write this because this nitrogen reduction equation is probably the most famous chemical reaction on the planet. Mountains of data on this reaction have been accumulated. And all the proteins in your body have been assembled via this reaction!