1. The planets orbit the Sun in pretty much a level plane. The most any of them stick out in their orbits is about 25^o.

   For example, if you go out at night, you'll see the recently-set Sun, the Moon, Saturn, and Jupiter are all in a line! (The ecliptic.) Even Jupiter's moons line up with this line, although the telescope we use reverses top and bottom.

2. The planets go around the Sun in the same direction

3. The planets spin in the same direction, except for Venus, which spins in the opposite direction
4. The spin axes of the planets--and of the Sun--all pretty much line up, although Uranus is tilted 90 degrees.

While something like Kepler's Laws turned out to result from fundamental, Universal, physical principles, these regularities of our Solar System are thought to result from history--there were forces that tended to make the Solar System the way it is. But there are also exceptions (Venus, Uranus) that prove this didn't result from a universal physical law.

One part of the nebula became more dense--maybe a nearby exploding star (a supernova) sent off a blast wave that compressed the gas--and then gravity started pulling things towards this center.

The conservation of angular momentum (remember, that's what makes the world go 'round!) means that any slight rotation of this nebula was magnified as gravity caused it to shrink. If parts of it were rotating in different directions, as they came together they would average out to one rotation direction--and no matter how slight, by shrinking, it would speed up, just like an ice skater bringing in arms spins faster.

So the shrinking cloud of gas starts spinning, and it also becomes a disk because orbits that are at angles tend to average out when they collide.