whats the best way?

Try a carpent cleaner. Machine.

Go down to local spray carwash and high pressure clean it. I do mine twice a year and it works real good. If you have stains pre-treat with dawn dishwashing liquid mixed with a little water then spray it.

carwash then go home and use a shop vac to suck up the extra water

I've always taken it to the car wash, but I seem to use too much soap. I end up rinsing it forever and not being able to remove all the soap. Afterwards the carpet even though it is very clean seems a bit hard instead of the softer feel.

Either way I just spray it down then let it sit out in the sun to dry.

If you want it soft, mix some fabric softer and water in a spray bottle and mist it , then hit it with the pressure sprayer or a hose.