How can i get better mpg on my truck?

I got a 78 Ford f150 but it only gets about 8-10 mpg. Is there any way I can improve my mpg? If I could get it some how up to 15 mpg I'd be a little happier. But I don't know if thats possible

Yes. Don't drive!

When a redneck tries to be a vegan

Sorry - not much you can do to double mileage-if it were doable Ford would have done it.

City driving, don't stop. Look at traffic signals ahead and adjust your speed so to roll on the green.
Highway, cruise at 30 mph in top gear.

You don't NEED a truck. Sell it and buy something that gets better mileage.

Air-up all the tires and clean-out the junk.

Not possible. Those trucks got the same whether driving at 25, 55, 95 or idle.

That year came with either a 351, 400 or 460 cubic inch engine. I had one with the 460 and it could tow a house and pass any thing on the highway except a gas station while doing it. Unfortunately there's not much you can do with it except keep your tires a bit over-inflated, drive very conservatively and keep it tuned up. You could put a 2bbl carburetor on it and advance the timing a bit and maybe… Just maybe eke 10 mpg out of it. Better to sell it to some other poor fool and get something with decent fuel economy. While you may not think you can afford to get a new truck, one way of looking at it is that for every 8,000 miles you drive you put about 1000 gallons of gasoline in the tank and spend $2500. Or so. If you drive 12,000 miles per year (national average is closer to 15,000) that's $3,750. In two years that's $7500. If you drove something that got 16 mpg you'd save half of that.

They sell throttle body EFI upgrade kits, that would be the only way to get a bit more on the gas millage by getting rid of the carburetor. I would swap out the engine to a more modern setup if the truck is nice and you want a daily driver.

A 78 Ford F150 with a 390 will suck that gas bad, no matter what you do to it. I would mod it with a 5L and OD trans.