If planning to mail the card, measure the envelope first and size the card accordingly (usually about 1/4 inch smaller all around). For the cleanest results, cut the paper with a craft knife on a self-healing mat (cut straight lines along a ruler). Some cards need the additional backing to conceal cuts or add weight; create a border by cutting the back piece slightly larger than the base, and layer patterned and solid papers.
Try the Popup Heart Card, Popup Proposal Card, 3-D Accordian Card, and Garland Card.
Resources: Paper and envelopes, paperpresentation.com. Bone folder, screw punch, and craft knife, all by Martha Stewart Crafts, michaels.com. White ruler, poppin.com.