Don't worry about perfection.
Realize that any handmade card will be welcomed and unique. It is a gift of your creativity and time. Cards are more personal than e-mail and allow you to stay in touch and let your recipient know that you're thinking of them. (You can show off a little bit, too!)
Play. It's only paper. You can paste over mistakes or use scraps of a card that didn't turn out to make another. Don't feel you have to follow the directions to the letter. Mix it up, use your own creativity and get your hands and work space dirty. Card groups or exchanges are a good way to force yourself to experiment. You can find them on the Internet or the classifieds in the back of cardmaking or papercraft magazines. Try using scraps and found objects to add to your card. You don't need to buy expensive embellishments in order to make cards, but try to use a good quality of card stock (available at all craft stores). This will yield better results for very little money.
Collect sayings and quotes. Some cardmaking and papercraft magazines provide quotes for your use. If you use a quote, be sure to credit the person who generated the quote. There also are Web sites that feature quotes and greetings. File them in categories in your computer, or if you have no computer, an expandable folder. Print them out as needed on your computer or hand-print. If your handwriting isn't perfect, don't worry. It adds to the charm of a handmade card. Try printing your greeting around a shape. Alphabet stamps also can be used for greetings, but spelling each word out letter by letter eats up a lot of time. Alphabet stamps are best used for one-word greetings or names. Rubber-stamped and rub-on greetings also are good investments.
Make multiples. When you make a card you like, make some more with the same elements or theme. You may not always have time to make a card as the occasion arises so you'll have them on hand if you make extras. Keep them filed in a card organizer, notebook or box with notes as to who the recipient was for each card. This will keep you from sending the same card multiple times to the same person.
Envelopes. Be sure you have an envelope that will fit the size of your card if you intend to send it through the mail. Odd sizes will require extra postage. Craft stores have prepackaged cards and envelopes, or you can buy templates to make your own envelopes. Decorate your envelope with scraps or die cuts or stickers that tie into the theme of your card.