Start by putting a few gentle/thrill rides on the edges of your construction rights. Then, build a shuttle-loop-type above the rides on one side, and another shuttle-loop-type above the rides on the other side. Make sure that they are exciting enough to meet the objective, and you will quickly have two coasters down, eight to go.
Keeping things tight, slowly move down the island with your roller-coaster building. Use lots of shuttle-loop-type and wild-mouse-type rides to get a high excitement rating with a relatively short track. Wooden coasters are a less effective choice here because, one, their support structure makes it difficult to see around them, and, two, they are generally less maneuverable than the steel coasters. Make the tracks go over/under/around existing rides and coasters for maximum effect. Add flat rides and paths around the coasters to bring excitement up even more. Building two Stations next to each other and synchronizing them will also boost excitement a lot.