Sealing the deal for a hook-up or a date?
If you want a date, go say hi, exchange names, say you would like to meet up for a date, and exchange contact info. Depending on the setting, you might also find out some of the guys interests and you can gauge what will make a good first date.
You can go through the dating process with the purpose of finding a job. When you first meet a guy you'd like to date, think of yourself as applying for a new job. You want to answer why the other guy would want to date you. You learn a bit about the other guy ("what it's like to work at that company").
The first date is like an interview. Here you find out a bit about each other and determine if it's a good fit. Sometimes you get the job during the interview, sometimes you're on a probationary period.
For a hook-up say "hi. you're hot. wanna fuck?" If he wants a hook-up that should usually be enough to seal the deal. You might want to tell him why you'd be a good lay-- you can do the splits, you have a huge cock, you can suck a bowling ball through a garden hose, you can go all night long.