Squad arranging
Various bits of fun I've detailed elsewhere involve moving Marines to a defence location and arranging them how you want (assuming they're going to stay in place). Here are some tips on doing the arranging.
Sharp dropping
When you drop Marines (i.e. make them dismount) and drive off, it's annoying if other nearby Marines try to hop aboard as you pull away. It seems to help if you perform the whole operation quickly. As the hog slows to a halt, dismount sharply and orbit the hog closely without stopping, pressing 'X' as you pass each passenger (or when you see the release message on the screen), then get back in quick and pull away. If anyone chases you, accelerate away and they'll soon stop.
Adjustments
If you want a Marine to move a few yards this way or that to fine-tune an arrangement, you can do it by carefully driving the hog at him so he dives that way. You can use this as a way of concentrating a squad or tidying things up. Don't let the hog get too slow when doing this, else some Marines may break formation and try to board it.
Getting a knot of Marines
If you want a group of Marines to stand very close together, you can use the following technique after moving them near the desired spot. With your hog on the spot, make passengers get out, then start up the motor again so nearby Marines all start closing to board, even if only briefly. After a few repetitions of this, they're all up close to the hog. Now gently angle the hog so you'll be able to drive off without squashing anyone, then make your final passengers dismount, and quickly drive off before anyone else gets in.
Getting Marines onto rocks
You can drop passengers on top of a rock if you can drive the hog up there. Or, you may be able to get a gunner to dismount onto a rock after backing up the side of the rock. With very low rocks you can even dismount a seated passenger on top. You might also get a Marine up by driving at him when he's next to it, causing him to dive up onto it.
Creative placement
Rather than placing the Marines in a relatively concentrated bunch, you could scatter them over a wide area, or maybe arrange a couple of small concentrations or something, perhaps for a crossfire. Be creative. Maybe it'll be interesting.
Chain-gun support
If you have anyone on a chain-gun, that's liable to make life a lot easier in any defence. However, you can reduce a chain-gunner's contribution by placing him well away from the main squad - which can be quite interesting. If you really want to rip the covies to shreds though, dual chain-guns are a lot of fun if you've got an extra hog available.