Great posts, a couple of my own, sorry if there are repeats:
Height matters differently for different heroes. I am now making controllers and defenders tall and scrappers and tankers short, because when in first person view (which I prefer in many situations) I can easily see over the other PCs, or they can easily see over me.
The missions where they tell you to kill "x" villains and then suggest where you night go to find that villain don't always REQUIRE that you go to that zone. If the mission says "Keep the peace in Perez Park" then you have to kill them in Perez Park, but if it says something like "Discover the secret formula: Kill "X" Vahzilok" and the contact says that you might look in King's Row or Perez Park for these baddies, you don't necessarily have to kill the villains in the suggested zone. Instead, turn around and whack the nearest Vahz near the contact. If it decriments the count, you're golden. The fastest mission I ever finished was one of these where there were 10 Vahz standing right next to the contact.
Click on a teammate and you will automatically target their target. (Think this was said already, but I keep running into people in teams that seem to always be getting in trouble because they are off soloing mobs in the group when we could all be combining efforts, maybe in 2-3 subteams, but at least not all individually.)
When you pick up hovering or flying and you are sniping at a Lt or Boss, look down before you take your first shot. Some can knock you from the sky (some minions too I think). I find it good to hover above power lines or train tracks when I snipe so that if they knock me down, I'm still not in easy melee range. I'd rather not fall all the way down to the ground where a couple of them are waiting to pummel me.
I've remapped my num keypad for most movement, and put "next target" and "closest target" on numpad + and numpad "enter." As I approach clusters of villains or areas of poor visibility, I cycle through by tapping + with my pinkie. You can do this from a safe distance, size up the group, and where visibility is poor you can actually detect enemies before you can see them. When you are ready to pick a target, click the numpad enter to go back to the closest, then cycle through to the one you want. You can drive and position yourself with the numpad steering keys while targeting without reaching over to the mouse or taking your fingers off the power keys bound to the numbers on the QWERTY keyboard.
I've also bound "look up" to numpad 9 and "look down" to numpad 3. Again, saves you from shifting your hands from mouse to keyboard for most steering, but admittedly this is a matter of style, and not an improvement for everyone.
