DIY car maintenance can save real money, but some tasks carry more risk than the savings justify for non-specialists.
Reasonably DIY-friendly: replacing air filters and cabin air filters, replacing wiper blades, checking and topping fluids, replacing a dead battery, and changing oil if you have the tools and a way to dispose of used oil properly.
Better left to professionals: brake work, where a mistake directly affects stopping ability; anything involving the timing belt or chain, where a mistake can destroy an engine; and suspension or steering component work, where precision tolerances matter for safety.
The general rule: tasks that fail safely if done imperfectly are reasonable to DIY; tasks where a mistake creates an immediate safety risk are worth paying a professional for.