Depends on what kind of "cold approach" you mean. A stranger in the street or at a store in the day time is different to one at a party or picnic, or to one at a club.
I'll give a little advice on cold approaching women
you don't know and aren't associated with in any way, and who are just out there minding their own business (like a woman walking on the footpath or at a shop.)
The best way to start a conversation in that situation is with a
comment of some kind. For example, if they're at a shop and have a bag full of 20 bananas, make a comment about it, or ask about it. At a shop, if you're looking at a shelf and a cute woman walks past, ask her which sauce would be best with whatever meal. Not only will it start a conversation, you should be able to work out how good of a cook she is

.
If you can't find something to comment on, or if you're walking past her, ask if you can get her opinion on something (works well if you're just walking past each other in the street). It's non-threatening, simple, and does a good job of getting women to stop and talk to you. Make it something
sincere. Once you've got their opinion, introduce yourself and go on from there as usual.