Hit level 30 with no idea what I'm doing
I want to build something decent for Jayce, but there are all these runes and I don't know which ones are the best ones.

Any SIMPLE tips?

Armor pen marks, flat ad quints, flat armor seals, and MR per level or flat mr glyphs for jayce.

That's probably the most common rune setup for him.

Those are pretty standard ADC runes, too.

I'd just search for a Jayce guide on Mobafire or Solomid if you want more info. They always include rune setups, though some guides are better than others.