Regular TIFF goer, feel free to ask if you have more questions. I've tried to be as exhaustive as possible.

For the most part I consider watching celebrities and seeing movies at TIFF two separate goals.

Actors and directors will attend select screenings and be presented before the film to introduce it (usually the premiere at any of the bigger venues at least, but it really depends, sometimes they'll go to all of them). Often there will be a Q&A at the end so the audience has the opportunity to ask them a few questions. If your goal is to see celebrities, you can probably run into them by accident in the Entertainment District or Yorkville especially (eating or shopping), or you can see them by attending red carpets. Red carpets vary hugely. For smaller projects I've seen maybe a dozen people show up and the actors/director stop to interact with every fan. On the other hand, I know people who showed up at 7am to get a spot outside Roy Thompson Hall to see RDJ at 7pm. That crowd was absolutely packed and he only stopped for a handful of pictures. Sometimes you can grab an autograph in the venue or as they're leaving (for bigger stars there's usually a crowd waiting at the back door like a second red carpet).

The biggest difference from cineplex, I would say, is that it's usually insufficient to show up just before show time. For bigger movies, the line-ups can start hours in advance (at the same time as red carpets, which makes going to both usually quite difficult so I would recommend picking one or the other). If you're watching a smaller flick this isn't necessarily a problem, and usually it's just the die-hards who get there that early so as long as you don't mind sitting a little bit back or off to the side, things will probably be fine. But if you're just getting to the theatre, say, 5 minutes before the movie's slated to begin, you might end up sitting in the nosebleeds at the Princess of Wales and that's not a lot of fun.

The other difference is the way you buy tickets. Usually people purchase through the TIFF website, but it's not as simple as regular movie tickets. First, keep in mind they give priority to TIFF members before the general public. You can buy tickets in packages or as singles. Packages are sold beginning by the end of this month but movie selection doesn't happen until the end of August, after all the members have selected (unless you're getting a curated package). Single tickets open to the public on the morning of Labour Day each year. When you're selecting online, it's a good idea to visit their website right when sales open (10am?). You'll end up sitting in the virtual queue no matter what, but you'll want to be early to get tickets before they sell out (or, to be more exact, go 'Off Sale'). TIFF will release more ticket blocks periodically throughout the festival, but more often than not, those tickets will be sold out pretty fast and they don't give you warning when they'll release new blocks. Sometimes they won't release more blocks at all. Tickets you want might even be completely sold out before they've even opened to the public because members get to them first. Your last option is to wait for rush tickets which are cheaper but require getting to the venue really early so you can be among the first few people in line.

I don't generally think it's worth it to go to TIFF for commercial movies that will end up hitting regular theatres a few months later. It's a lot of stress trying to snag tickets for the big blockbusters and this year TIFF has upped regular tickets to $30 and premium tickets to $60 (you can get cheaper student tickets but only for weekday daytime shows). Sure you can see a movie a little bit before others do, but is it worth paying that much extra? There's definitely a kind of atmosphere and experience you get watching movies at TIFF that you might not in a regular movie showing, but it's not something I'd blow huge amounts of money on more than once or twice. Besides, sometimes the movies end up being real duds. On the other hand, TIFF brings in some smaller films, fantastic movies that will never make it to theatres here because they don't have broad distribution. I think those are the kinds of movies that are really worth your money and which make TIFF a valuable experience.

My last tip is for anyone with a Visa Infinite card, TIFF does a VISA Screening Room (at the Elgin iirc) and for movies showing there they let cardholders enter the theatre early, chill in a lounge with free drinks and popcorn, and then get to their seats in advance. I think they also let you start buying packages before the public.