How do you grow pot fast?

The straightest answer I can give you is that if you want good pot you don't grow it fast.

Ganja needs to have at least a 4 week vegetable state to allow proper growth of the stalk and twigs, the smaller the plant the less bud it'll produce and then at least a 2 or 3 week flowering stage for good buds.

Then there's the drying out and curing of the buds, say around maybe 4 weeks total there.

Basically any way you cut it your looking at around 4 months time to grow and produce good quality buds. There are somethings out there such as MiracleGro and the like that will help the plants grow SLIGHTLY faster but all in all it may only shave a week off the total time at the most. You can also use Plant Hormones but this isn't in my opinion at least a good idea as strange things can happen to plants when you start screwing around with they're hormonal balance. Its best to leave that alone as well.

I have had pot grown in half that time (2months) but it was rush grown, tasted rush grown, was harsh as sucking down broken glass and the high was....well it wasn't.

You can go for speed but if you do quality drops down the toilet, if you want good bud then just buck up, deal with the time it takes to grow good plants and in the end you'll find it was worth the extra wait.