A tip for color pallets is to generally start out with either a warm or cool palette (Or both, you can use warm and cool colors to reflect light and shade.) Not really a rule but it'll just make things faster when you want to get some basic shading done. You could also start out in gray scale, if the key thing you want to get across is a lot of contrast but always shift hues (use complementary colors like yellow and purple)... You want the art to look vibrant so also avoid desaturated colors.
But those are just some rules, always use some form of reference for environments to get an idea of which colors you are going to use and always experiment to find what works for you.
There's tons more that goes into this stuff if you want to look up color theory, but for pixel art I'll also recommend you check out Pixel Architect and Pixel Overload on YouTube for more comprehensive tutorials.