Game Of Thrones: 8 Ways Season 6 Spoilt The Winds Of Winter (And 3 It Didn't)
3. Daenerys Conquers The Dothraki And Sails For Westeros

After six seasons, it finally happened. After going from the Dothraki Sea to Meereen, via the Red Waste, Qarth, Astapor, Yunkai, and back to the Dothraki Sea and eventually Meereen again, Daenerys Targaryen has set sail for Westeros, intent on ruling the Seven Kingdoms.
Considering where Daenerys is at the end of A Dance with Dragons, and that she will eventually need to get a move on to Westeros in the books, it's probably safe to assume that something similar will happen.
The difference in terms of Daenerys being surrounded by a khalasar in ADWD is that Drogon is by her side, whereas he'd flown off and left her on the show. With a huge dragon next to her, it's less likely that she'll be taken as prisoner to Vaes Dothrak, but it could be that she returns there on her terms, as a means of securing herself a Dothraki army to help her take Westeros.
We're already headed for a Battle of Meereen, although that won't have Tyrion Lannister, and will have Barristan Selmy (given his show death, there's a good chance this is where the books will kill him off). And we know that Team Daenerys will win that, not just because that's what happens on the show, but because, well, she's Daenerys Targaryen.
As for the details on how she travels to Westeros, they're a little more muddied in terms of show/books crossover. Dorne sent Quentyn Martell to Meereen as a way of aligning with Daenerys, and he was burnt to a crisp, and they're now more concerned with another supposed dragon.
In terms of ships, Victarion Greyjoy handily arrives in Meereen with the Iron Fleet, just as the siege is starting. If he doesn't survive using the dragon horn (which seems likely, because it's hard to see him taking control of Dany's dragons), then Dany will have a fleet of ships all ready to take her to Westeros, much like the closing moments of Season 6.