Acclimatization takes a minimum of two to three days, but a lot of tourists ignore this. You arrive and you're already dying to sleep at two in the afternoon because of the flight and the time zone change, but you try to start doing tours and active stuff right away. By the end of the week you're completely drained, and your vacation's basically shot. It's better to just rest at the hotel on your first day, maybe meditate on the beach without any stress, let your body adapt. Then your energy will come back and you'll actually have a decent vacation.
Another pretty common mistake is buying souvenirs and stuff without comparing prices and without haggling. Maybe it's obvious, but people really do end up paying three times more than they should because they're buying everything in tourist shops right next to the hotel. If you want decent prices, you need to go to local shops, markets in regular neighborhoods where actual Turks shop. And always haggle, even if it feels awkward - it's totally normal practice there.