If you can watch from the start...
...do. The pacing is tighter in the TV show than the books so it won't be a "wade through" (most of the minor side stories and lore didn't make the cut, and the only mention of lemon cakes is one fan-service joke where Olenna subtly teases Sansa). While Season 1 is pretty close to the books' main story, even skipping that leaves a couple of issues:
- At least one added show-only character (Ros) who you won't recognise
- Most of the characters look very different to their book descriptions. Many (e.g. Tywin) you'll be able to figure out from context or dialogue, but beyond the first few episodes the show expects you to recognise all the main characters' faces
- Many characters have subtly different personalities from the start, and you get a different perspective on the characters, including scenes that couldn't fit into the books' viewpoint chapters like this one (Robert Baratheon's war stories)
Best to enjoy it all as a different story, inspired by the books. Not least because many of the things that have happened in the show beyond A Dance With Dragons (especially in Season 5) can't happen in future books, because characters are in the wrong place, or don't exist, or are too dead, or aren't dead enough...
If you really can't wait that long...
...for example if you have very limited time, an impatient viewer could skip to the start of Season 4. You'll miss a lot of great scenes (it starts shortly after Edmure's wedding), but in terms of not being confused by adaptation changes from the books, it's a good place to get on board:
- Most of the storylines that were heavily changed from the books in earlier seasons (e.g. Arya's, Theon's, Ramsay's, Margaraey's, Jon and the wildlings) have at this moment drifted back to being pretty similar to the books, and so easy to pick up. I'm struggling to think of any major characters who are doing anything fundamentally different at this moment to what they do in the books (if I've forgotten any, drop me a comment!).
- The most fundamental changes haven't happened yet. Season 4 is where storylines start to irreversibly diverge from the books.
- Also, being the first episode of a season, it re-introduces the characters and main storylines somewhat, which will help orienting yourself.
You'll still probably spend some time getting your head around changes, but it'll mostly be things you can figure out, for example:
- Characters that are missing and have been subsumed into others (e.g. there's no Garlan Tyrell, so Loras is the Tyrell son who subjected to marriage politics, no Strong Belwas, and no Bloody Mummers, instead the Boltons have a bannerman called Locke loosely based on Vargo Hoat)
- Characters whose personalities are different or differently presented (you'll figure most of these out, e.g. Littlefinger is more of a brothel mogul and Arya is less of a sociopath)
- A couple of things hinted at in the books are made explicit in the show in earlier seasons and you're expected to know them (that Loras is gay and was in a relationship with Renly, and that Ramsay's torture of Theon included castrating him)
- A few relevant small details worth mentioning: the characters Arya had killed in Harrenhall are slightly different, Asha Greyjoy is renamed Yara to avoid confusion with Osha, and Balon Greyjoy is still alive.
Lots of other details were different in earlier seasons but not so much in ways that would confuse a viewer starting here.
Of course, if you're doing this, you might want to skip back a couple of episodes to Season 3 Episode 9, "The Rains Of Castermere", which is famous/notorious and one of the highest rated of the entire show. But if you're doing that, you should skip back an episode or two further to appreciate some of the foreshadowing that made it so good plus get to know a TV-show only character they created for that storyline. And if you're doing that, you might as well skip back further to Season 3 Episode 4 for the awesome Astapor scene. And if you're doing that, you should consider skipping back a few more because that too has some clever build-up scenes, and if you don't, the Ramsay scenes in these episodes won't make any sense. And if you start at the beginning of Season 3, you might as well skip back to Season 2 Episode 9 for the awesome Blackwater episode, but if you're doing that, you should skip back further else Arya's very different scenes in Harrenhall won't make sense, and if you're doing that...
Whatever you do, I'd suggest not starting after Season 4, because in Season 4 we begin to get some fundamentally different storylines and strong hints about things beyond A Dance With Dragons (particularly in Bran's storyline).