The major food flavours -- salty, sweet, sour, bitter, spicy and umami -- all play off each other, balancing or enhancing the other flavours. You can make any dish taste better by knowing the science behind it, and this chart can help.
Cook Smart's flavour star graphic shows the interplay between the flavours, with black lines showing how to level out a flavour and light grey lines revealing how to bring the flavour out more. If a dish is too sweet, you can balance it by adding a bitter ingredient or a spicy one. If you want to enhance the sweetness, add a salty or umami ingredient. (Adding more umami-rich ingredients can amplify the flavour in most dishes, actually.)
Check out Cook Smart's detailed guide to flavour balancing and enhancements.
A Study of Flavour Profiles [Cook Smarts]