Oktoberfest

Probably too late for tickets. We went 2 years ago on a weekday afternoon. We were able to sit at a table until the time the table was reserved for. I think that was 5:00 p.m. My impression of Oktoberfest was that it reminded me of a State Or County Fair. Substitute beer tents for livestock exhibitions. There are rides, food booths and souvenir booths in addition to the beer tents. My advice would be that if you are inclined to go on rides, do it BEFORE you drink beer!!

Don't need tickets and don't miss it. You must be seated at a table to get a beer. Minimum size is 1 liter (a tad more than a quart). Many tables get reserved by big outfits (BMW, Siemans, ets) to entertain clients, customers, employees in the evening, but you can poach in the afternoon until the people who reserved the tables show up. http://www.oktoberfest.de/en/ is the website with all the activities. Check out English/Oktoberfest online dictionary. I especially like the Bavarian word for guys who hang out and drink other people's unfinished beers. Other people at your table will be stangers on the first beer, and your "best friend for life" by the third.
It takes place in the Theresienwiese park. It has its own subway station. You can't miss it. Everyone will be there.

Get there early, eat as you drink, pace yourself (the beer is stronger that normal lager), and be prepared to meet people. This will be trip number 5 and we keep meeting people from past years and have been in communication with them since. If you see a group of Italians get a seat away from them but close enough to watch. They are hilarous! Prost!

Some actual practical advice: Do you have hotel reservations yet? That's the most important thing. Yes, you're too late for tickets. But here's the deal: Oktoberfest is a giant "fair" and you don't need a ticket to get in - where there are rides and foods and beer. But what people THINK of as Oktobefest - drinking beer in a giant tent - you will need tickets for unless you go VERY EARLY IN THE DAY. On weekends, arrive at opening -between 10am and 11am at the biertent to get in. On weekdays I've heard you can try to get in as late as 2pm. but you will only be able to stay until the people that reserved your table show up later in the day/evening unless you're lucky enough to get a spot at one of the unreservable tables. You can drink beer anywhere in Munich. Oktoberfest is a giant party, and you're going for the party. If you just want to drink good beer in Munich, I can give you a ton of suggestions.

We have been twice and didn't have tickets either time. Both times was on opening day. Yes, arrive early but with that you will Ave to wait out the youngsters. They drink very young there. We saw many teenagers drunk. You might have to become friends quickly with people because you cannot drink unless you are at a table. Tables are usually reserved well in advance. You can find people who will help you out. It is great fun! Ride the rides before the beer though. It can get ugly if you try the reverse. Lol!

Re: weekends... our group of five arrived at 9:30am on a Saturday. We had to wait outside the Hacker tent with a huge group of people for at least an hour and a half. We finally got into the "beer garden" section outside the tent, which was fine- got to order the same beer and food. However it was basically impossible to get into the tent- all full and/or reserved. One of the Germans in our group said the only way to get in at that point was to bribe the waiter with several hundred euros. Lesson being, go on a weekday.

Tickets? Do you mean reservations? As far as I know Oktoberfest doesn't require tickets either to get into the fest or the beer tents. Reservations, as far as I know are only for groups.
It's been a few years since I've been, so maybe things have changed. My best advice is to head to the tents in mid to late afternoon, after eating a full meal in the grounds. There is an early group that is usually being carted out by mid-afternoon, the tents fill up again in early evening and the lines get very long. Pick a tent and stay there. They are all essentially the same experience. If you try to wander to different tents, you will spend your entire night in line. You must be seated to order a beer and the whole place closes down early. When you sit down, get to know your neighbors as soon as possible. Your experience is largely dependent on interacting with the people around you (for good or bad).