Agree with Scissor Queen ... I actually have notes taped to the inside of my quilting thread box telling me which weights work nice together along with needle size and tension settings.
There are limits though ... even with fooling with both top and bottom tension I just can't get a 12wt on the top to work with anything lighter than a 30wt on the bottom. BTW .. I have a separate bobbin case to use just for "let's mess with the tension" sewing.