Finding accomodation is usually easy if you don't mind spending a lot of money. But most hitchhikers don't have a lot of money, so then there are several other options:
You can bring your tent and sleeping bag and you'll basically be free to sleep anywhere. Beware that in most countries it's not legal to put up your tent anywhere. It's legal in Scandinavia though.
It can happen that your driver offers you a place at his or her house to put up your tent. It can also happen that you get a place offered inside.
Hospitality Exchange networks
Hospitality Exchange networks require a bit more planning.