The quickest way ....
From Las Vegas, drive north on Interstate 15 approximately 35 miles to State Route 169. The cut-off is well marked. There is a Paiute Indian Reservation Tobacco Shop and small casino at that exit. It is a great place to make a pit stop before you go on to Valley of Fire. Drive east on Route 169 for approximately 15 miles. This takes you to the west entrance of the Valley Of Fire. The drive through is about 10 miles in length and take you to route 167, the North Shore road.

The most scenic way ....
The route along the North Shore Road takes a little bit longer. It is very scenic. Along this this route, there are 4 marinas that you can stop at and have lunch or just look around. There are some excellent vistas of Lake Mead from the North Shore Road, but most of them are from a distance. This route takes you through  colorful desert vistas. Along the way are several extinct volcanoes, outcroppings of the bright red Navajo Sandstone and dozens of intriguing geological formations. 

From Las Vegas, drive east on Lake Mead Blvd., past Frenchman and Sunrise Mountain approximately 15 miles to Route 167. Turn north (left) on route 167 for about 40 miles. Two Miles past the Overton Beach cut-off, turn west (left) on Route 169.

The best way to go is to do both. I recommend that you start with the quickest route and you go back to Las Vegas along the North Shore Road.

In the photo at the top we are looking at the road which goes to the White Domes.