JP256 wrote:READ THE NOTAM!
What I haven't seen anyone mention yet is the part of the NOTAM where you are directed to fly at a very specific airspeed (90 knots, or max cruise if you can't do 90 knots, in which case they also recommend you arrive between 7:00 and 7:30 AM!) until you are basically on short final and have been assigned your colored "dot" to land on. Before I flew into Sun-N-Fun, I practiced flying the pattern at 90 knots until short final, and asked my local tower crew to "surprise" me with either "numbers" or "Intersection" (1800 ft down the runway) as my required touchdown points. It wasn't quite the same as the 3 dots at SNF or OSH, but darn good practice. The first time I did that, I had a hard time slowing from 90 on short final and making the touchdown point. Glad I practiced - got an "Attaboy" from SNF tower for the "real thing"...
You asked about good day/time to arrive. Sunday arrivals for the past two years at OSH were a total zoo. A bunch of idiots flew in that had apparently never even heard of the NOTAM, and busted into the pattern flying directly into landing traffic with 3 on final, 3 on base, and 7-8 on downwind... Of course, when they finally saw the traffic, they started a climbing turn directly into the middle of the pattern.
READ THE NOTAM!
The other thing is that by mid-morning on Monday, the homebuilt and GA camping areas were full. By early Monday afternoon, even Vintage camping (and the far Southern end way down past the Ultralight area) were filled up. Until Wednesday (when some folks finally left), there was no room for aircraft camping, unless you just happened to arrive just as someone else left. Thursday and Friday were OK until late Friday afternoon, and then it was packed until Sunday morning (last day - pretty much nothing going on except the airshow).
In my book, the best days to arrive are the Friday or Saturday before the show starts. Friday is a lot lighter traffic, but Saturday is still way better than Sunday/Monday.
READ THE NOTAM!
One more thing... Be sure you have PLENTY of fuel on board when you get to RIPON for the arrival procedure. If someone screws the pooch and closes one (or more) runways for a while, traffic stacks up VERY quickly, and you may be holding for a long time (2 hours or more delay is not unheard of). Best plan is to immediately divert to one of the many local airports and wait it out on the ground. But whatever you do, do NOT arrive there with just enough fuel to get to OSH... Delays are pretty much "normal procedure" for any time of arrival.
And one last point: READ THE NOTAM!
I'd add to that, READ THE NOTAM!

Seriously, it has in it just about everything you need to know.
Practice before hand is valuable--know what power settings achieve 90 knots. Trim for that airspeed in level flight. You're coming in at 1800' MSL (1000' AGL), and you want to easily maintain that. I suggest following a road as practice to follow the railroad track from RIPON to FISK--it's not exactly a straight line, but close. Then practice landing on a specific point, because you're asked to land on the dot that ATC (tower) assigns. Practice right hand patterns, because if you're given 27, that's a right hand pattern, and it's close in. If you're given 36 or 18, it could be 36L/18R (a normal runway) or 36R/18L (a taxiway that is a lot narrower than a runway).
When tower tells you to start your descent, which they will about mid-downwind for 27 or 18, that's a good time to get slowed down to your approach speed. It's a relatively tight pattern, and it's a lot easier if you're at your approach speed by the time you're turning base. Then hold that approach speed to land on your assigned dot--but if you're going to miss it, don't worry about it. You have plenty of runway, no matter what. As many times as I've landed on 36, I can't recall being told when to descend, but it's a base entry, so you'll want to get down soon enough so that you can turn final at about 14-1500' MSL, 4-500' AGL.
It's a good idea to practice go arounds, because that does happen. Some honyock will fail to taxi off into the grass, or someone will prang (I watched that happen 3 times last year--none of the ones I saw hurt anyone, but airplanes were hurt and the runways got closed for awhile). If tower says "go around", do it immediately. I've had to do that, when the airplane in front of me refused multiple tower directions to exit into the grass.
So far in many years of going to OSH, I've only had to hold once, and that was for about 45 minutes. I always go in with a surplus of about 3+ hours of fuel, so fuel has never been an issue. It's not that fuel is pricey at OSH, because it's not--pretty normal these days. But holding and watching the gas gauges go down would be really uncomfortable.
And don't talk on the radio unnecessarily! Don't respond to most ATC calls with words, just do.
And have fun! That's really what it's all about.
Cary