The most important key is with the cardstock to only purchase solid core so that the paper is the same color through and through.
There are a lot of different types and weights of paper to use when making paper flowers. Here are the weights of paper I use for my flowers:
Cardstock: 50 – 80-pound paper. I do not ever go above 80-pound because the paper is too thick to curl without wrinkling Crepe paper: 60-180 grams weight