Young dogs, and dogs not used to cars may not enjoy the experience of travelling at first, but if journeys are initially kept short, and the dog ends up somewhere fun like a park, they are likely to get in the car eagerly after a few trips. It also helps to take the dog for a walk, or play in the garden first, so he can get rid of some energy, and relieve himself if he needs to.
Some dogs are naturally good travellers, and lie down on the floor. Other dogs need to be taught to that they should sit quietly and not make rude comments to passers by, human or canine. Have someone travel with the dog to remind him of his manners if he is a bit rude. Barriers preventing dogs from getting to the front of the car make travelling safer, but even so drivers need to be able to focus on the road rather than being distracted by the dog.
It's also safer to train dogs to leave cars only after permission, if you live in the city, and it makes it easier for you to stay in control, especially if you have more than one dog. Again, use a short lead for dogs getting out of cars where there's traffic or passers-by, its safer.