Now, i don't have that much of a problem when it comes to restaurants/bars or places selling clothes. The problem comes in other places where the girl has to keep moving from one spot to another, and has many customers to serve at once. In this case it's a sort of arcade/bowling/family oriented place, it's loud and with lots of people, so striking a long conversation doesn't seem to be the way to go, or at least not an easy thing to build considering all the distractions. Any ideas?

I'm also curious. Especially waitresses and sales girls who kind of have to be friendly to you while they're working.

With regard to waitresses, there's Zan's method, I've not had opportunity to try it but it looks pretty cool. I've just copied and pasted:
When I see her conning toward us, I immediately engage a buddy across
the table in seemingly deep conversation. I make sure to face my body away
from her.
When she comes up and asks us what we would like to drink, I ignore her
for a few seconds or so. Then I glance in her direction and pretend I am just
now seeing her for the very first time. Immediately, I show great interest in
her—as if she were a new discovery. I glance quickly at her body, just long
enough for her to notice, then turn myself fully around to face her. A big smile
and a wink, and the game begins.
HER: What can I get for you?
ZAN: [Ignoring the question] Hello, I haven't seen you around before.
What's your name?
HER: My name is Stephanie. What's yours?
ZAN: I'm Zan. And I will have a gin and tonic. (Big smile)
So far I've broken the ice a bit and, by exchanging names, she has given me
the implicit right to be more familiar with her. So the next time she comes
around, I smile and wink again.
ZAN: You again? Wow, you sure like to hang around us, don't you?
HER: [Laughs] (some stuff)
ZAN: (Some other stuff)
HER: (Some other stuff)
ZAN: (As she is leaving) I bet you'll come back again real soon. I can see
it in your eyes.
HER: (Smiling) Yeah, I can't resist.
Now I have established a cocky funny theme—her wanting to hang around us
and that is why she keeps coming back to our table. Of course, she has to
come back to our table: She's the waitress. And when she does, I smile at her
and give the other guys a knowing look in front of her as if to say, "See, I was
right." All along, I strive to make the interaction come off like I have known her
for a long time. This establishes a level of familiarity that usually takes several
meetings to build.
So now, after a while, I will say something like:
HER: Can I get you another drink?
ZAN: (Smile, wink) You know what? You're kinda cute. I think I'm going to
call you.
HER: You think so, huh? You don't have my number.
ZAN: Why, you're right! Okay, tell me and I will write it down.
HER: [Smiling) Not a good idea. I have a boyfriend.
ZAN: (Pretending to write) Whoa, slow down. I didn't quite catch your
number there. You better repeat it for me. Lets see . . . 555 . . .
HER: (Laughs and rolls her eyes)
The absurdity of this exchange is that there is no way she is going to give me
her phone number in front of a bunch of my friends. No girl would. But her digits
are not the goal just yet.
Now she and I have a rapport, in a manner of speaking. And I've made
myself memorable enough that the next night we go there, she'll recognize me.
This way, I can walk up, put my arm around her, and continue with my usual
'You would make a good girlfriend for me" talk. And since everything is said in
a half-joking manner, she doesn't know if I'm really hitting on her or if I'm just
fooling around. So when I return:
HER: (Laughing) Oh no! Not you again!
ZAN: Stephanie, my sweet! Hey, listen, sorry I didn't return your call last
night. You know how it is. I'm just a busy guy.
HER: (Playing along) Yeah, I'm really mad about that.
This gets the whole table laughing, including her. And its back on again for the
evening.
Later
ZAN: You know what, Stephanie. You're a terrible girlfriend. In fact, I can't
even remember the last time we had sex. That's it. We're through.
ZAN: (Pointing to another waitress) She's going to be my new girlfriend.
HER: (Laughing)
ZAN: [Playing with my phone] You are now downgraded from Booty Call
#1 to Booty Call # 10.
HER: (Laughing) No, please, I'll do anything to make it up to you.
And later still:
ZAN: [Motioning for her to come over and pointing at my knee] Stephanie,
come and sit down. I'll tell you a bedtime story. [Smile, wink]
I have used that last line for years. It is gold.
Some of you guys are probably thinking, "Okay, now what? How do you
transition from funny ball-busting to more serious, romantic, sexual talk?"
It's simple, actually. At some point, I just talk to her quietly alone. Remember
to turn on the bedroom eyes.
ZAN: [No longer cocky funny] Stephanie, do you want me to call you?
HER: You know I have a boyfriend.
ZAN: That's not what I asked. Do you want me to call you?
HER: Tempting, but I can't.
ZAN: Sneak away with me, girl. I'll take you higher up the slopes of Parnassus
than you have ever been. Etc.

_________________
One cannot lose what one has never had.

For waitresses and sales girls i would usually open them with questions about the food or drinks, in the case of the waitress, and the clothes or other products they sell in the case of the sales girl. From there i build up a longer conversation.

In this case i'm talking about i really have no idea how to properly open the girl, it's an arcade/bowling/family oriented type of place. I might go from time to time to play some arcade to pass the time, but again, i just can't come up with something for some reason. I already found a good hour when there's not many people around.