Individuality
I firmly believe that twins should be treated as individuals rather than a unit and dressing them the same all of the time is not cute.
The first question asked when speaking about twins is "are they identical?" The term identical is given to twin types who have been created when a single egg, fertilised by a single sperm splits into two separate but genetically identical embryos however this doesn't actually result in two babies who are identical in every way. Identical Twins (also known as Monochorionic Twins) often look very similar and many are hard to tell apart but their personalities and emotional needs can be very different.
Fraternal twins (also known as Dichoronic Twins) often look no more alike than regular siblings especially if they are boy/girl twins making it easier to treat them as individuals.
Just because twins are born at the same time or look the same it doesn't mean they are not individuals and they should not be treated as a one half of a pair. Do not assume that because they are twins they will automatically have the same likes and dislikes, interests or personalities; once again they are likely to be very different.
It is very important to encourage individuality from the outset and refrain from referring to them as "the twins". Use their names and encourage others to do so. Dressing them the same can be amusing but not when it causes everyone to confuse them and call them by different names. How annoyed would you be if everyone kept forgetting your name?!
Do not expect twins to share one toy. Babies and toddlers have to learn to share and it's no different for twins.
As your twins get older it is important for them to undertake separate activities and make friends of their own. Your twins will have built a strong bond as babies and toddlers from all the time spent together and they may not be comfortable with separation. However, when the time is right and as your twins get older it's important to help them gain some independence from one another.