Make a List

You'll make your Christmas list and check it twice, three times and more over the coming months!
I use an excel spreadsheet with the following columns:
Name
Gift (idea or actually purchased)
Dollar amount

Since we also exchange stocking stuffers, I add 2 additional columns with the stocking stuffer and dollar amount.
I also color code the form (RED means it's not yet purchased or made and GREEN means I have need it.  I record the dollar amount to assist with keeping me within my budget and have it self total at the bottom

NOW, make a list of anyone you give gifts too
Mother, father siblings, spouse/children the mailman, your co-workers.  YES, list everyone even if you are only giving them a plate of cookies! 
Print the list and keep it in your purse.  When you make a purchase, record it on the form immediately.  You can update the computer version periodically. 
This has become an invaluable tool for me as I use it to record ideas (sometime early in the year).  If I  can get a bargain early in the year,  also keeps me from purchasing an item for someone whose gift I already have.