I have so many to buy for that I start in January, if I see something that I know 1 of them would like. I usually do a reasonable amount of pondering, and purchasing, in the summer sales (lovely handbag for DSis 1 year, and DSil another year, for a song!). I like to make some presents too when I have time, so they need to get started early (I started knitting a blanket for DH's aunt about 4 years ago - I just never get a chance to sit with it anymore to finish it, it's only about halfway done lengthwise, but very easy knitting when watching tv, how I long to just watch tv at night again!!).
Things that are ok to pick up now are stocking fillers if I see quirky things or get bargains in socks, underwear etc or nice stationary in back to school sales; PJs for DH, DD and I; start putting together non-perishables (both for our house and for the Lions Club collection - I aim to give them essentially a week's shopping for a family so will get doubles on stuff like coffee with extra free, or get a 3for2 and put the spare into that box etc all autumn). And try to find a couple of bottles of naice wine for DH and I to enjoy on Christmas Day (he'd buy decent wine, €10-12 "big brand" bottle rather than €4.99 Lidl everyday drinking (we have a few specific ones we get which are actually very drinkable at that price), but I like to see if I can find a really nice one as a treat - we'll only drink 1 bottle anyway, so I think it's worth it. And I like to try to find a half bottle of desert wine for pudding, which I will probably drink mostly, but I don't drink it the rest of the year).
And I tend to keep an eye out in general for things that I know would suit particular people. So something to do with sailing or outdoors for 1 uncle, I got a lovely metal bookmark at a market in Brussels last month (instead of the book token he's got for the past 10 years) for DH's uncle, 1 aunt loves music, another is really into gardening (and autumn clearances in garden centres can be surprisingly good hunting grounds - not just for gardening things!), 2 guys are mad about Monty Python and Mr Bean, 2 couples are either just finished organizing their own home or about to embark on it - so any good deals on homewares are good for them too. There's a couple of babies that small clothes are always welcome, and the somewhat bigger children are generally reasonably non-fussy about what they want from us (1 loves Hello Kitty, another loves a particular sport, an older one loves playing piano and HSM so I'm getting her sheet music of that this year - but something age-appropriate either clothes or toys-wise can be bought whenever I see a good option.
While I am not yet embarking on DD's main presents (Christmas, and Birthday on 26th December) or her clothes (which she will help choose), or DH's as he has everything and is sooo hard to get ideas for (and hasn't yet thought about it, apparently), I am making decent progress on the rest.