just follow the instructions very carefully. Typically you have to fill out the form, cut out and include the UPC, and include the packaging slip. Mail it all in and wait. There are typically deadlines, like you have to mail it within 30 days of purchase. I've never had one denied, but I have goofed up and threw away the UPC with the box :-P
Yeah, As long as you follow the instructions to the letter you wont have any issues. just note that it can take 2-3 MONTHS to get your rebate.