What's the best way to cover a dark paint colour with a lighter one?

No, just go ahead and paint........

More than likely, you will have to use a good primer to cover the too dark paint.

To prevent the dark color from bleeding through use a primer .

Tracy more than likely it will take a primer as stated above in the comments. Did you know you can purchase a primer tinted to to the final color you want on your wall. You might consider this.

What color did you paint It? Because based on the color of paint,it can possiblyaffect the color of primer. If it's a red paint, or any version of red, you will need to use a gray primer. If it's orange, a slight blue based primer.

I would prime it before putting your top coat on.