There are usually multiple strategies to successfully completing a scenario; these can be discussed on this article's talk page.
To complete Dragon's Cove, you will need to finish the roller coasters one by one and make money off them, since its most likely you'll run out before finishing all 5 roller coasters. Start off with finishing the Steel Roller Coaster, since its the easiest to get the excitement rating up (because of the Vertical Loops and coaster tracks going through it). You can build it underground. After that, open the park and build a path towards the ride (If you need to make more money, build a Shuttle Loop coaster to keep money rolling in).Now that should be enough to keep your money over debt, but build some gentle rides too to please the timid guests. The order of finishing roller coasters to complete should be the following:
Steel Roller Coaster
Vertical Drop Roller Coaster
Suspended Roller Coaster
Suspended Looping Roller Coaster
Bobsled Roller Coaster
Remember to have many coaster tracks going through loops, since it increases the excitement rating a lot for rides. Don't make the rides too intense, otherwise the excitement rating drops. The last three roller coasters are the trickiest to build, since they have high nausea and intensity ratings usually, and as for the Bobsled, it crashes off the track! Make sure you leave some space for the bobsled roller coaster, such as the water area to the left of the map, since it is difficult to build. Make sure you save before building the Bobsled, and open the rides to the public to make more money, unless it crashes with guests on the ride, but is safe without them. It is very easy to run into financial trouble in this park, since the loan can only be doubled. Try not to clutter other rides in with the roller coasters, as this can make building the roller coasters very difficult. Often, just having the coasters go through the hills and trees will make it exciting enough to meet the requirements.