Act 1 is a fantastic showcase of speed. You'll immediately encounter long downhill slopes that allow Sonic to reach top speed. Use these to launch yourself over gaps and through loops. The Caterkillers are a common enemy; they can be destroyed with a single jump or Spin Dash. Watch out for the large, spinning platforms; time your jumps to land on them safely and use their rotation to reach higher areas.
There are many opportunities to take high paths, which often lead to more rings and power-ups. A hidden 1-Up Monitor can be found: after a long downhill section that leads into a loop, you'll be launched upwards. Instead of going straight, try to land on a small, hidden platform to the left, which contains the extra life. This Act is all about maintaining momentum and enjoying the exhilarating speed, but keep an eye out for secrets.