ppl hot soak, ppl cold soak, typically the hotter the water the more the denim shrinks. you're jeans are sanforized (pre-shrunk) so they'll shrink a bit in length .25 to .5", you can try stretching the inseam when they're wet.
washing - you can do it in your bathtub with a woolite or a more gentle detergent, turn inside out, i) move them around in soapy water, ii) leave for a bit, repeat i and ii 4 or 5 times, drain, soak in water, drain, hang dry, or you can use the washing machine, but washing machines do generally give vertical fades/lines where the jeans crease in the wash, which may not be what you're after. you'll want to hang dry either way, more shrinkage occurs in the dryer.