Here are some common strategies:
What does this person need? To some people, there is no higher satisfaction when giving a gift than to have the giftee say, "That was exactly what I needed." The gift giver took notes months in advance of Christmas whenever they were with the giftee. Need new pot holders in the kitchen. Wished they had a throw pillow for their favorite chair. Broke the handle on their favorite coffee mug. These gifters pay attention to the details and always have a keen eye out for the perfect gift.
What does this person like? These gifters know their giftees well and can identify their favorite things. Big fan of trashy romance novels? Likes loud Christmas sweaters? Collects bulldog figurines? Knowing and identifying these likes assure you'll buy a gift that is a hit.
What would this person never get for themselves? Some people intentionally pick things that their giftees would never think to buy for themselves. Skydiving lessons? A set of rollerblades? Some snazzy pink suspenders? Sounds perfect.
What's on sale? Buy a bunch of stuff that is on sale or looks cute -- some candles, some Blu-rays, a picture frame, some books, a nifty calendar. Then look at your list of people you need gifts for and match column A to column B. Got Aunt Marge a candle last year? Looks like she's getting the calendar this year. Make sure all of your boxes get checked.
Which category do you fall in?