Don’t wash them in hot water, don’t put them in the dryer!
It depends on whether they’re regular non-stretch jeans, or if the jeans have lycra/spandex/any kind of stretch in them.
To keep non-stretch jeans from shrinking, wash them in warm or cold water and always hang them out to dry. This is a good idea for all the clothes you have that you don’t want to shrink (or fade!). If you wear jeans with some stretch in them, you can wash them in warm or cold water too. If you’ve noticed the stretch jeans are getting really baggy/loose at the end of the day, you could put them in the dryer on a LOW cycle, and take them out while they’re a tiny bit damp. This will tighten them up, but not significantly shrink them. Otherwise, your best bet is to hang them out, every time!
One other tip: When you take your jeans out of the dryer, and before you hang them up, pull and tug and yank on them in whichever direction you don’t want them to shrink. Every little bit helps!
Don’t wash them in hot or even warm water, and DO Not Put them in the dryer.