Plan the paths first
Lay a main path from the gate down the middle, then add side paths to each ride. Use polished andesite or stone bricks so the path stands out from the grass. Guests, and your friends, will follow the paths naturally.
Use bright concrete colours
Red, yellow, blue and pink concrete make rides look cheerful from far away. Alternate white and a colour for striped roofs and awnings. Keep the ground green and calm so the rides pop.
Build the rides in the round
A merry-go-round is a circle: use a disc for the floor, poles around the edge and a cone roof. A Ferris wheel is a big circle standing on its side, with spokes from the middle and small coloured cars hanging from the rim.
Make coasters from long diagonal lines
A roller coaster is a long upward line, a drop, a loop and a flat finish. Build the track three blocks wide, and add white pillars under the high parts so it looks held up. Place the loop first, then connect the rest to it.
Light it for the evening
Put lanterns on posts along the paths and hang some inside the stands. Sea lanterns on top of the fountain and the drop tower glow nicely at night. Light also stops monsters from spawning in your park.
Add small details
Balloons made from small spheres on fence posts, trees around the edge and ticket booths by the gate all help a lot. Small touches make a park feel busy and alive.