Best method to make a piston in minecraft?

if it builds fine but won't push something, that's usually the block. max 12 in a line, and some never move at all - obsidian, chests, furnaces, anything that holds items.

Top row 3 planks, middle row cobblestone / iron ingot / cobblestone, bottom row cobblestone / redstone dust / cobblestone. Then add a slimeball on top of it in the grid if you want a sticky piston.