Did Season 1 have previews? I am not sure. I cannot find any previews for Season 1 episodes.
Season 2 had that promo with the live action sword.
Season 3 had episodic promos, general Cartoon Network stuff though.
Jake vs. Me-Mow
Season 4 had this one
with the exception of Burning Low, which had this misleading one.
The whole of Season 5 had this promo below.
Season 6 now has this one:
It’s evolved from our goofy main logo into this beautiful thing.