You really have to plan it pretty far out. Ideally, you should book lodging in Jan/Feb at the latest.
I cannot stress this enough: Go on a weekday and not a weekend. Reserving spots in tents is kind of like a lottery but your chances are much better M-Thur than Fri-Sun. We did attempted at two tents and got reservations at the Hofbrau tent. This website will be your friend:
https://www.oktoberfest.de/en/beer-tents/reservations-at-oktoberfestOn a separate evening, we wandered into the Loewenbrau tent and got some tables by sheer luck. Still, there were plenty of spots in the outside Biergarten (and the other outdoor Biergartens next to the tents normally have availability).
There are a ton of carnival rides there, but I highly recommend visiting die Oide Wiesn. Which is basically all the old-school rides and they're like 1.50 EUR a piece. It's super nostalgic and feels like you're at an old fair.
It's a blast, albeit a crazy expensive and exhausting one.