You have plenty of posts telling you how to do it if you want to do it.
For a contrasting perspective:
I find it adds too much stress and hassle. I hate to add on hours and hours of extra driving at the end of the day, trying to find some place legal to park in a booked-up area, or getting up in the wee hours to move camp. For me it is much more relaxing to plan ahead, whether that means a boondocking area on a forest road or a reservation in the park.
Winter is a whole different story, though. Someone mentioned the California coast. I spent a couple winters there. During the school year, weekday nights, there are lots of open sites! And the weather is 65-70 degrees and sunny, from Santa Cruz to Mexico.
