Tip 1: freefall without damage. Jack a copter, if you've already got your base set up it'll have a helipad on top. You can jack a copter at the airport. The airport is here on the lower left part of the map right at the bottom. See that big building?

Go there and you're bound to find a flyable vehicle. If not, use some cheats to spawn one.
Get in your helicopter, fly to your hideout and put it in your garage. In Saints Row, you keep every vehicle that enters your garage. If your vehicle is destroyed it just respawns in your garage good as new. If you alter it at the car shop, it's automatically saved. This way, in case you fail this diversion, you will be able to do this repeatedly without having to go find ANOTHER plane or copter.
Anyways, get a copter out of your garage, fly as HIGH UP AS YOU POSSIBLY CAN, bail out and you'll be in a free fall. Press triangle to open your parachute, and when prompted press triangle to do the base jumping diversion. The goal of this is to land in the red bullseye marked on your map. Holding up while in the chute makes you catch wind. Pressing down makes you stall and go slower. Not holding anything makes you go and normal speed and allows you to turn around and position yourself easily.
Land on the Saints car that's parked in the bullseye. The trick is to look at your stars for doing this trick. In order to get no damage, you have to have three golden stars while landing in the bullseye. Do that and you get no damage from freefall at any height. Useful because you will fall A LOT in SR2.
Tip #2. Next do the insurance fraud activity in Redlight District. You start out at the Redlight District and the insurance fraud one isn't too far away. Finish all 6 levels of insurance fraud at this location and you get INFINITE SPRINT. It doesn't break the game like you would assume but it makes things ten times less annoying.
Tip #3. You want to do whacky and crazy stuff? Let's start you out at Let's Pretend. For some reason Volition opted to hide Let's Pretend in a weird to find mall location. In order to get to the mall, go to the north island and then the Downtown retail area. There's a section called Nob Hill. See that white square thing on the map? THAT'S the mall. This location is just a block away from the Downtown Condo.
Find the entrance to the mall. You take an elevator up into the Ultor Retail Mall.
Find the shop Let's Pretend. There's another good shop too called I Hate Myself for people want to dress up as a depressed emo.
At Let's Pretend you can find doozies such as this:
[youtube=560,345]rep0Pq3l9aU
[/youtube]
Go to other stores located on the map to see what works for you.
This yt should show you how to get to Let's Pretend:
[youtube=560,345]p-AbGVeDSrk[/youtube]
Tip #4. Which gang do you start out with? It doesn't really matter, but most think Samedi -> Ronin -> Brotherhood is the best in regards to narrative and story, and I agree, but Brotherhood is the best one and also the HARDEST gang so I suggest going with them first. When you beat Brotherhood you get their fighting style, which are nothing but wrestling moves.
Coupled with infinite sprnit, no damage from falling, endless customization options from all the shops and wrestling moves in your repertoire you should find Saints Row 2 to be a pretty fucking crazy game. The only difference is that you have to WORK to make the crazy in SR2, SR3 this isn't really the case.