The first step is to use the search bar at the top of the forums. It's there so there aren't dozens of these threads opened every week asking questions that have been answered. Please use it in the future
There's lots of basic bolt ons like the Outlander/Lancer aluminum intake manifold & throttle body, a "cold air intake", long tube headers, etc. Then more advanced mods like the dohc head swap that allows for better upgrades like the Evo 8 cams, intake manifold, and even a simpler head to bolt a turbo kit to. Some people drop a complete Evo engine in. Just depends on your experience and how far you want to take it. It's all been done many times so it's just a matter of searching to find the info you need.