When you make a purchase(s) for rebate item(s) make sure those purchases are separate because you have to send the original sales receipt.
I had purchased two items that were both Rebate on the same sales receipt and I forgot at the time when I purchased them. I step out on faith and send one Rebate to a company with the original sales receipt and the other Rebate to the second company with a photo copy since the original went to the first company. Today I got a letter back from one of the companies stating they need the original sales receipt no photo copy.
When you do send your Rebate make copies of everything. I make a copy of the form once I fill it out, then a copy of the sales receipt, then a copy of the bar code before I send all originals to the company. I staple them all together and put in a file titled "Sent Rebate" and I put the date I mailed it. When I get my Rebate check back I pull that Rebate information out of the "Sent Rebate" file and write on it the date I received the check and file it in the "Received Rebate" file that I hold for a little while before trashing.