Decanting styles

i usually pour it slowly down the sides, and it seems like that allows maximum air exposure without being rough with the wine. the only downside is you have to watch the sediment or you'll have half of the decanter covered in dirt

Depends on the wine. These are my general guidelines:

If it has thrown a lot of sediment or has other weird gunk in the bottom of the bottle (I check with a small flashlight shined through the bottom of the bottle), pour it slowly to avoid disturbing that stuff, stopping and discarding the sediment and gunk before you pour it into the decanter. Once that's done you can double decant the wine, pouring it back into the bottle or into another decanter to maximize the exposure to air.

If the wine is very old, it generally should be decanted carefully, not only because of the sediment but because the wine itself may be quite delicate. In fact, decanting really old wine is often best avoided.

If the wine is young and free of significant sediment, pour it fast and into the middle of the decanter to expose it to as much air as possible.

Gonna have to agree with Doug's recs here...when older, you don't want to agitate the wine. But with a youngster that needs air, let it rip right into the middle of the bottom of the decanter. And don't be shy with swirling the decanter vigorously...

If you buy a brand new wine from the store. Does it really need to be decanted or is it pretty much ready to go?

generally speaking, you're gonna want to decant "brand new" wines. if it's a very recent vintage (06, 07, 08) decanting can't really hurt the wine and can only really help.

there are bound to be exceptions, but it's a pretty reliable rule of thumb and you can take it to the bank for any young cab, syrah, or merlot.

i always tell friends who are new to the hobby to have some fun with it. grab 2 decanters, splash decant 1/3 of the bottle real hard into a decanter, slowly decant another 1/3 into another decanter, and drink the last 1/3 out of the bottle. You'll notice very little difference between the 2nd and 3rd options but will notice a big difference between the 1st and 3rd.

I use an Aerolatte micro-whip and can tell a difference with a mere 30 second whirl in the glass. It does work well and is very portable unlike a large decanter.

Get a Vinturi and decanter. Place the Vinturi on the decanter and pour the wine.