There are usually multiple strategies to successfully completing a scenario; these can be discussed in the comments below, written down in an additional section of the article or added to an existing subsection.
The first thing to decide upon is where to build your rides. If you do not mind building rides inside the castle, then you should make use of the pathways and start building. However, if you are a perfectionist who wants to keep the castle intact, there is plenty of space around the outside of the castle. Make sure to block off any pathways that are not needed. If there are enough rides in the park, 1,200 guests should not be too difficult to achieve by the end of Year 3. Also be careful of the Wooden Reverser Roller Coasters, as they have a tendency to stall and crash on one of the coaster's hills, especially on those that are on the right of the park.