Depends how much money you have. I am a college student and don't make enough for major upgrades.
If you are just wanting to start small go through the basics of replacing the plugs,wires, and cap. Battery and generally cleaning of the engine, checking for worn parts. And then if you have a mechanic or shop you trust their word, take it there and have them give it a once over for anything else since there is several other things that might still be stock and not have been replace in the past 18 years.
But really past that you can look at getting tires and suspension. I know my 89 323 is needing new suspension in the future because it doesn't take bumps well, and the tires are always good to check for tread.
Basics stuff there you can normally start off naturally
