start from the area of Heraklion perfecture where the two main historic sites are but avoid staying in heraklion city as not good at all for holidays only for shoping and the museum. from that point on you will need a car as Crete is a big island and if you are looking for historical places you will have to drive around. Rethymnon and Chania really nice with their old town (Chania) the long beach (Rethymno) and the villages around. not staying there so i can think of small but nice sites to visit or recoment beaches. for bars for sure you will not have a problem.
If you are up to for youth tourism etc try Malia or Chersonisos. Agios Nikolaos has a couple of small sites to visit like Spinalongka etc.
Dont know for how long you will be in the island but try to divide your stay in half East and half West Crete so as you will not be driving up and down. that way you will see a bit of both to get a first taste and in the future you come again to see more and more detailed along with the small details you will miss out

We have stayed on Crete a number of times and love it. Mostly the north/south western side is our favourite. Elounda is nice and quiet with lovely restaurants, opposite is Spinalonga Leper Island, worth a visit. Ag. Nik lovely to walk around for the shops etc. There is a small very deep lake in the middle of the town with restaurants around it and a small platform where entertainment is laid on, like Greek dancing etc. You can walk around the lake and view it from the top of the hill, very pretty at night. Our all time favourite city though is Chania. So much to see and plenty of shops, park, restaurants and bars, the harbour is lovely to stroll around at night and take a carriage ride. There is even a Cinema there which screens all the latest films (before we get them in the UK) - quite an experience (Greek subtitles).... the cobbled lanes are lovely to walk around with shops of all kinds. If you go further up the city near the University to the Catacombs there is a lovely cafe/bar which has fantastic views of the north west coast (they also sell fabulous choc. cake), mostly frequented by locals as the visitors do not know it is there. The beaches along the north and south west side are fantastic - must to visit are Elafonisos, Falasarna, Paleochora. Agia Marina is predominantly touristy but not unpleasant and Platanais is much more livelier, the further west you go the quieter it is though, very nice! Hope you find something on Crete - you will not be disappointed. Having said that Rethymnon was our least favourite place! There is so much to see you have to go back more than twice!!