For starting camo, go with either M81 Woodland (basically just standard woodland camo) or Woodland MARPAT. I, personally, would choose the MARPAT simply because of it's digital pattern, but it's up to you.
I recommend adjustable two-point slings such as the VTAC sling or VCAS sling. The Magpul MS2 or MS3 is also good if you want to have a two-point sling with the option to convert it to a one-point sling on the fly.
Lots of people swear by single-points because they offer retention and generally allow the user to shoot left or right handed unimpeded.
I recommend two-points because they offer excellent retention. If you want to climb a ladder or carry something with both hands, a single point leaves your rifle dangling around with the muzzle unrestrained, while an adjustable two-point can be sinched up so that the rifle is held tight to the body.
A quality I look for in any good sling is wide webbing. 1" wide slings tend to cut into the neck or shoulder if you're using them with a heavier rifle, while a 1.5" wide sling will distribute the weight a bit better.
I recently picked up the padded version of the Blue Force Gear VCAS sling, and it's pretty comfy compared to my older VTAC sling.
The VTAC is more adjustable because it has a "tail," the bit of loose webbing that is a result of tightening the sling down all the way, while the VCAS has less adjustability but no "tail" to get tangled on stuff.
If you're running an M4 or a standard rifle, like G3, MP5, G36, AK, etc then you can find plenty of sling options available. If you've got an unusual rifle (MP7, P90, AUG) you might want to look into a sling designed for that weapon system.
A good place to see various sling features shown off is youtube. If you find a sling you like search youtube for a video and watch the user actually put the sling through its paces. With two-point slings there's a bit different set of movements needed to effectively shoot left handed, which you might not like in comparison to the freedom of movement that a one-point sling offers.
Additionally, take a look at the hardware that the sling ships with. Some slings are set-up so that they come ready to attach, while others need some special hardware or shackle to attach appropriately. For example, the G36 has a few sling points built onto it that you might need a specific type of hardware to attach to. So you might buy a sling that would attach to an M4 easily out of the box, but might need special hardware to work with the G36.
Slings are one of those things that are hard to know if you'll like until you actually run a game or two with them. My advice would be to pick up a cheap KZ ("KZ" = Klyzon, or some manufacturer) one-point AND a cheap two-point on Botach.com. You can probably get both for less than $30 before shipping. That way you can try both types out and you won't be out a lot of cash, plus you'll have an extra sling for that extra rifle that we all know is in your future.
I personally recommend the Mission Spec Irene Adaptive Sling. It's a single point sling, do its easier to switch shoulders with, that can convert to a two point sling, for weapon retention. However, you can't really fire your weapon while it's in two point mode. They come in Black, Coyote Brown, and Foliage Green, and retail for around $35 dollars on Airsoft GI.