I can totally quote you Hkaur.
Always ask for price, duration and route before stepping on a gondola. A gondolier must be able to reply in English and to show you where he'll take you on a map. If premises are not nice, don't bargain but just walk away.
Sharing the fare is a good idea: I'd agree on a price for the boat, THEN look for someone to share it with.
Inner canals are usually more interesting than Grand Canal, where waves/noises/pollition and people staring at you can sometimes be disturbing. And you have a wonderful view of the whole Grand Canal from a much cheaper, long-lasting and comfortable busboat too, after all. But if a gondola in Grand Canal is what you want, just ask several different guys and you'll find what to go for.
A gondola ride is a must here... I don't know, gondolas were historically used by common people to cross Grand Canal or by wealthy ones to be carried around, or during special celebrations and I can't keep from thinking that they never were so unreasonably expensive as they are today. Gondola rides are a sort of a tourist stuff nowadays, have one if your Venice dream includes it but do not consider it as a must. Musts often let us loose some sense in what we're doing, same as just wandering around and getting lost in this reasonably safe town is probably giving us more than spending one week forcing ourselves to visit one tenth of the Musts one can find here. Again, if a world famous spots marathon is what you need, be happy with it but don't feel like you have to do it.
In case gondolas appeal you and so living our everyday life does, a nice alternate to a gondola ride might be what we call "traghetto", which means crossing Grand Canal on a shuttle gondola. That's what Venetians do (we do not usually think of a Gondola ride in a lifetime, neither for a marriage which would now feel like bragging around or so) when bridges on Grand Canal are far (we only have 4) or when we don't like to walk on them.
A gondola traghetto is 50 cents/person, it lasts 1 minute and it takes you somewhere. I'll never forget my excitement as a child of 5 when mummy took me to the Rialto market on a traghetto gondola for the first time.
You can have 100 gondola traghetti for two persons with 100 Euros (and 100 gondola minutes versus 30)!
Venice road signs point to traghetti, most maps indicate them too with a dotted line across Grand Canal. Venetians know their timetables and choose an appropriate walking route depending on which traghetto is working on a particular time.
Last but not least: the Gondolier corporation is extremely conservative and only men are allowed to pass the TEST neede to become one, although no written rule states that this job is just for men.
A German girl dreaming to drive a gondola applied to the TEST several times and always failed year after year, out of unknown details; I finally saw her riding a gondola down my canal last summer and waved at them, she apparently made it at least as a private gondola driver for an hotel:
http://www.mrnews.it/2007/04/primo-g...nna-a-venezia/
I'd happily skip all male gondoliers in order to have her carrying me around for my first gondola ride, as a reaction to such a narrow minded, sexist view.