There's a lot to be said for staying in set. I've found a nice mix of opening lots and staying with a couple of sets if its going well works nicely.

1. I open
2. they hook because I'm interesting (Note: I must be interesting!)
3. I see if they're interesting
3a. they are boring I leave [goto step 1]
3b. they are intersting
4. I determine the group relationships, see what the score is, if anyone is available
4a. the group doesn't contain any valid targets
4ai. eject [goto step 1]
4aii. make them into friends, take some numbers, maybe they have hot friends, or know people [goto step 1]
4b. the group contains targets
4. I determine their logistics, see if they match with mine
4a. if the logistics are tricky, I number close or just eject [goto step 1]
4b. if the logistics match, or their plans are indetermined / weak, we do something together
5. I stay in set until either something goes majorly wrong, or I am ready to leave. Whilst in set I can still open short other sets (and its a good idea to do so, like at the bar), I just say hi, introduce myself, be friendly, kino, but always excuse myself and return to the long term set which is going well at the current time. You can always reopen the other sets later.

Steps 1 - 3a (They are boring, I leave) I determine within the first 5 mins
Steps 1 - 4 I do within the first 5 - 20 mins.
Step 5 you're in it for the long haul!

Doing this the other night came out with about:
20 opens, most of which were just saying hi to people
4 sets I spent a short amount of time with (5 - 20 mins)
2 sets I spent a significant amount of time with and closed (30 - 60 mins)