Adult family members: I pay attention to things they say they'd like to have. Sometimes I just buy ahead & have birthday, Mother's Day, & Father's Day presents bought ahead of time too!
My MIL always tells me things she or FIL need/want & sometimes months ahead of time. She knows I'm a planner! I just gave her something for Mothers Day that I've had since Veteran's Day that she admired in a store when we were shopping! She always wants a list from us, especially now that we have DD. I keep a list on the computer year round & give it to her around Thanksgiving. She takes grandchildren to Wal-Mart or K-Mart to the toy section. They show her everything they want and she makes notes. Later she goes back and picks out a few things they wanted. We get little surprises too, so we don't know everything we're getting!
Child family members: Sorry, you are getting clothes unless your mom says otherwise! I just ask the parent's what size. Now the kids are getting older & like certain brands, so I either buy from that store or give a gift card for that store.
Other gifts: I just pick something I think they would like. I don't mind if they re-gift, because I sometimes re-gift too!
DH refuses to tell somebody what he wants unless he REALLY wants it. He said "It's the thought that counts, so I shouldn't have to tell you what I want." However, he is the one who is never excited at Christmas and sometimes never uses something he got because he doesn't like it. I never know what to get DH because if he wants something, he usually just goes and buys it himself. Last year I really paid attention & he had more gifts under the tree than DD did! He was really surprised and seemed to love it all! I wish I could do that well every year. Bless him, he usually buys me things that he would like to have...I guess it really IS the thought that counts!