73 dart tuneup info needed

need.more.info.

new build? new to you car/motor? was running fine and now it's not? has it been sitting? has somebody else had their filthy paws in it? etx, etx, etx

have you done any basic diag on it? checked plugs, chased vacuum leaks, leak down, compression test, checked for a hung float dumping gas, dirty air filter, plugged exhaust, and so on and so forth.

performed a basic tune up?

how did you come to the conclusion that the mileage is poor?