Have a look at The Baby Wearer for a lot of information about different styles of carriers and a guide to choosing one that will suit you and your baby.
You can find lots of ways of wearing slings and wraps by online searching - and don't forget to browse Youtube as well.
If you can make it to a sling meet you will always find people willing to help you sort out a new carry. And if you can't, then a visit to the Baby Carriers Down Under forum is sure to help you on your way!
With twins or more, how often do you find that they both (or all) want - or need - to be held at the same time.
There are a number of Youtube videos showing how to carry twins at the same time. One of the easiest ways is a tandem hip carry.
This is the "Jasmin's tandem hip carry" and you can find detailed clips of how to make and wear the carry online.
Amanda and her delightful twins are demonstrating the carry. She used a long wrap and a pair of large sling rings that she bought here.
The Unpadded ring sling is probably my overall favourite baby carrier - it is infinitely adjustable, light to carry, easy to nurse in, flexible in carrying positions (at least 7 that I can think of off the top of my head), cool in hot Australian summers and I make them in lots of fantastic fabrics! Different positions make carrying any baby from newborn to toddler comfortable and convenient.
A stretchy pouch (also known as a tube sling) is our favourite for winter or any time we want to snuggle. It is simple to put on, easy to nurse in, very light to carry and fairly flexible for carrying positions. I have a stretch cotton pouch for summer days when we want to use a pouch. This sort of carrier is my daughters' favourite - they have a rainbow of them!
When we are heading out on a long bushwalk, I often start wearing a knit wrap. This is a long piece of fabric that is tied over both shoulders and distributes the weight across shoulders, back and hips. It is light and very adjustible; however it takes some practise to tie well and you need help for some of the back positions until you are competent with it.
Some fabric, a straight stitch sewing machine and a little
time is all that is needed to make yourself a tube sling or mei tai.
With a pair of
sling rings, you can
quickly make your own ring sling.
Link to sling rings
Jan Andrea's wonderful Sleeping Baby website has links to a number of good tutorials for making yourself a baby carrier.