I had a 1.8L sohc in my 94 Protege, probably pretty similar. Mine responded decently to a little more ignition timing advance (just twist the distributor) on regular 87 octane fuel. Gas mileage and engine response were improved. You really want to have a timing light to see how much you're advancing, and keep an ear out for detonation especially in hotter months or driving uphill (more load, more propensity to knock.) JIC, scrawl a mark where the distributor attaches to the engine at the stock location so that you can quickly go back to stock if you have to.
Beyond that, you start spending money, and I'm not sure what kind of budget you have to mod a car this age.
